Computer Troubleshooting ¶ 

Your first PC repair or upgrade can be pretty intimidating. What if it doesn't work? Worse still, what if the PC goes up in flames the first time you turn it on? Set your mind at ease. This isn't rocket surgery. Any reasonably intelligent person can repair or upgrade a PC with a high degree of confidence that it will work normally afterward. If you use good components and work carefully, everything usually just works.

Still, stuff happens. So, although we provide more detailed troubleshooting suggestions for specific components throughout this guide, we thought it was a good idea to summarize early in the guide some basic troubleshooting steps to cover the most common problems that occur during a system repair or upgrade.

Possible problems fall into one of four categories, easy versus hard to troubleshoot and likely versus unlikely. Always check the easy/likely problems first. Otherwise, you may find yourself tearing down the system again before you notice that the power cord isn't plugged in. After you exhaust the easy/likely possibilities, check the easy/unlikely ones followed by hard/ likely and, finally, hard/unlikely.

Most problems that occur during repairs and system upgrades result from one or more of the following:

Cable problems ¶ 

Disconnected, misconnected, and defective cables cause more problems than anything else. The plethora of cables inside a PC makes it very easy to overlook a disconnected data cable or to forget to connect power to a drive. It's possible to connect some cables backward. Ribbon cables are a particularly common problem, because some can be appear connected, yet be offset by a row or column of pins. And the cables themselves cannot always be trusted, even if they are new. If you have a problem that seems inexplicable, always suspect a cable problem first.

Configuration errors ¶ 

Years ago, motherboards required a lot more manual configuration than do modern motherboards. There were many switches and jumpers, all of which had to be set correctly or the system wouldn't boot. Modern motherboards auto-configure most of their required settings, but may still require some manual configuration, either by setting physical jumpers on the motherboard or by changing settings in CMOS Setup. Motherboards use silkscreened labels near jumpers and connectors to document their purposes and to list valid configuration settings. These settings are also listed in the motherboard manual. Always check both the motherboard labels and the manual to verify configuration settings. If the motherboard maker posts updated manuals on the web, check those as well.

Incompatible components ¶ 

In general, you can mix and match modern PC components without worrying much about compatibility. For example, any IDE hard drive or optical drive works with any IDE interface, and any ATX12V power supply is compatible with any ATX12V motherboard (although a cheap or older power supply may not provide adequate power, which means you need to visit Computer Power Supplies and Protection). Most component compatibility issues are subtle. For example, you may have installed a 1 GB memory module in your system. When you power it up, the system sees only 256 MB or 512 MB because the motherboard doesn't recognize 1 GB memory modules properly. It's worth checking the detailed documentation on the manufacturers' web sites to verify compatibility.

DOA (dead-on-arrival) components ¶ 

Modern PC components are extremely reliable, but if you're unlucky, one of your components may be DOA. This is the least likely cause of a problem, however. Many novices think they have a DOA component, but the true cause is almost always something else usually a cable or configuration problem. Before you return a suspect component, go through the detailed troubleshooting steps we describe. Chances are good that the component is just fine.

Here are the problems you are most likely to encounter when you repair or upgrade a system, and what to do about them:

Problem: When you apply power, nothing happens ¶ 

  • Verify that the power cable is connected to the PC and to the wall receptacle, and that the wall receptacle has power. Don't assume. We have seen receptacles in which one half worked and the other didn't. Use a lamp or other appliance to verify that the receptacle to which you connect the PC actually has power. If the power supply has its own power switch, make sure that switch is turned to the "on" or "1" position. If your local mains voltage is 110/115/120V, verify that the power supply voltage selector switch, if present, is not set for 220/230/240V. (If you need to move this switch, disconnect power before doing so.)
  • If you are using an outlet strip or UPS, make sure that its switch (if equipped) is on and that the circuit breaker or fuse hasn't blown.
  • If you installed a video adapter, pop the lid and verify that the adapter is fully seated in its slot. Even if you were sure it seated fully initially and even if you thought it snapped into place the adapter may still not be properly seated. Remove the card and reinstall it, making sure that it seats completely. If the motherboard has a retention mechanism, make sure the notch on the video card fully engages the retention mechanism. Ironically, one of the most common reasons for a loose video card is that the screw used to secure it to the chassis may torque the card, pulling it partially out of its slot. This problem is rare with high-quality cases and video cards, but is quite common with cheap components.
  • Verify that the main ATX power cable and the ATX12V power cable are securely connected to the motherboard and that all pins are making contact. If necessary, remove the cables and reconnect them. Make sure that the latch on each cable plug snaps into place on the motherboard jack.
  • Verify that the front-panel power switch cable is connected properly to the front-panel connector block. Check the silkscreen label on the motherboard and the motherboard manual to verify that you are connecting the cable to the right set of pins. Very rarely, you may encounter a defective power switch. You can eliminate this possibility by temporarily connecting the front-panel reset switch cable to the power switch pins on the front panel connector block. (Both are merely momentary on switches, so they can be used interchangeably.) Alternatively, you can carefully use a small flat-blade screwdriver to short the power switch pins on the front-panel connector block momentarily. If the system starts with either of these methods, the problem is the power switch.
  • Start eliminating less likely possibilities, the most common of which is a well-concealed short circuit. Begin by disconnecting the power and data cables from the hard, optical, and floppy drives, one at a time. After you disconnect each, try starting the system. If the system starts, the drive you just disconnected is the problem. The drive itself may be defective, but it's far more likely that the cable is defective or was improperly connected. Replace the data cable, and connect the drive to a different power supply cable.
  • If you have expansion cards installed, remove them one by one. Remove all but the video adapter. If the motherboard has embedded video, temporarily connect your display to it and remove the video card as well. Attempt to start the system after you remove each card. If the system starts, the card you just removed is causing the problem. Try a different card, or install that card in a different slot.
  • Remove and reseat the memory modules, examining them to make sure that they are not damaged, and then try to start the system. If you have two memory modules installed, install only one of them initially. Try it in both (or all) memory slots. If that module doesn't work in any slot, the module may be defective. Try the other module, again in every available memory slot. By using this approach, you can determine if one of the memory modules or one of the slots is defective.
  • Remove the CPU cooler and the CPU. Check the CPU to make sure that there are no bent pins. If there are, you may be able to straighten them using a credit card or a similar thin, stiff object, but in all likelihood you will have to replace the CPU. Check the CPU socket to make sure there are no blocked holes or foreign objects present.
  • Remove the motherboard and verify that no extraneous screws or other conductive objects are shorting the motherboard to the chassis. Although shaking the case usually causes such objects to rattle, a screw or other small object can become wedged so tightly between the motherboard and chassis that it will not reveal itself during a shake test.
  • If the problem persists, the most likely cause is a defective motherboard.

Problem: The system seems to start normally, but the display remains black ¶ 

  • Verify that the display has power and the video cable is connected. If the display has a noncaptive power cable, make sure that the power cord is connected both to the display and to the wall receptacle. If you have a spare power cord, use it to connect the display.
  • Verify that the brightness and contrast controls of the display are set to midrange or higher.
  • Disconnect the video cable and examine it closely to make sure that no pins are bent or shorted. Note that the video cable on some analog (VGA) monitors is missing some pins and may have a short jumper wire connecting other pins, which is normal. Also check the video port on the PC to make sure that all of the holes are clear and that no foreign objects are present.
  • If you are using a standalone video adapter in a motherboard that has embedded video, make sure that the video cable is connected to the proper video port. Try the other video port just to make sure. Most motherboards with embedded video automatically disable it when they sense that a video card is installed, but that is not universally true. You may have to connect the display to the embedded video, enter CMOS Setup, and reconfigure the motherboard to use the video card.
  • Try using a different display, if you have one available. Alternatively, try using the problem display on another system.
  • If you are using a video card, make certain it is fully seated. Many combinations of video card and motherboard make it very difficult to seat the card properly. You may think the card is seated. You may even feel it snap into place. That does not necessarily mean it really is fully seated. Look carefully at the bottom edge of the card and the video slot, and make sure the card is fully in the slot and parallel to it. Verify that installing the screw that secures the video card to the chassis did not torque the card, forcing one end up and out of the slot.
  • If your video card requires a supplemental power cable, be sure to connect it and make sure it snaps into place.
  • If the system has PCI or PCIe expansion cards installed, remove them one by one. (Be sure to disconnect power from the system before you remove or install a card.) Each time you remove a card, restart the system. If the system displays video after you remove a card, that card is either defective or is conflicting with the video adapter. Try installing the PCI or PCIe card in a different slot. If it still causes the video problem, the card is probably defective. Replace it.

Problem: When you connect power (or turn on the power switch on the back of the power supply), the power supply starts briefly and then shuts off ¶ 

All of the following steps assume that the power supply is adequate for the system configuration. This symptom may also occur if you use a grossly underpowered power supply. Worse still, doing that may damage the power supply, motherboard, and other components.

  • This may be normal behavior. When you connect power to the power supply, it senses the power and begins its startup routine. Within a fraction of a second, the power supply notices that the motherboard hasn't ordered it to start, so it shuts itself down immediately. Press the main power switch on the case and the system should start normally.
  • If pressing the main power switch doesn't start the system, you have probably forgotten to connect one of the cables from the power supply or front panel to the motherboard. Verify that the power switch cable is connected to the front-panel connector block, and that the 20-pin or 24-pin main ATX power cable and the 4-pin ATX12V power cable are connected to the motherboard. Connect any cables that are not connected, press the main power switch, and the system should start normally.
  • If the preceding steps don't solve the problem, the most likely cause is a defective power supply. If you have a spare power supply, or can borrow one temporarily from another system, install it temporarily in the new system. Alternatively, connect the problem power supply to another system to verify that it is bad.
  • If the preceding step doesn't solve the problem, the most likely cause is a defective motherboard. Replace it.

Problem: When you apply power, the floppy drive LED lights solidly and the system fails to start ¶ 

  • The FDD (floppy disk drive) cable is defective or misaligned. Verify that the FDD cable is properly installed on FDD and on the motherboard FDD interface. This problem is caused by installing the FDD cable backward or by installing it offset by one row or column of pins.
  • If the FDD cable is properly installed, it may be defective. Disconnect it temporarily and start the system. If the system starts normally, replace the FDD cable.
  • If the FDD cable is known-good and installed properly, the FDD itself or the motherboard FDD interface may be defective. Replace the FDD. If that doesn't solve the problem and you insist on having an FDD, either replace the motherboard or disable the motherboard FDD interface and install a PCI adapter that provides an FDD interface, or, if your motherboard allows you to boot from USB devices, purchase a USB external floppy drive for the purpose.

Problem: The optical drive appears to play audio CDs, but no sound comes from the speakers ¶ 

  • Make sure the volume/mixer is set appropriately; that is, that the volume is up and CD Audio isn't muted. There may be multiple volume controls in a system. Check them all.
  • Try a different audio CD. Some recent audio CDs are copy-protected in such a way that they refuse to play on a computer optical drive.
  • If you have tried several audio CDs without success, this may still be normal behavior, depending on which player application you are using. Optical drives can deliver audio data via the analog audio-out jack on the rear of the drive or as a digital bit stream on the bus. If the player application pulls the digital bit stream from the bus, sound is delivered to your speakers normally. If the player application uses analog audio, you must connect a cable from the analog audio-out jack on the back of the drive to an audio-in connector on the motherboard or sound card.
  • If you install an audio cable and still have no sound from the speakers, try connecting a headphone or amplified speakers directly to the headphone jack on the front of the optical drive (if present). If you still can't hear the audio, the drive may be defective. If you can hear audio via the front headphone jack but not through the computer speakers, it's likely the audio cable you installed is defective or installed improperly.

Problem: SATA drives are not recognized ¶ 

  • How SATA (Serial ATA) drives are detected (or not detected) depends on the particular combination of chipset, BIOS revision level, SATA interface, and the operating system you use. Failing to recognize SATA devices may be normal behavior.
  • If you use a standalone PCI SATA adapter card, the system will typically not recognize the connected SATA drive(s) during startup. This is normal behavior. You will have to provide an SATA device driver when you install the operating system.
  • If your motherboard uses a recent chipset e.g., an Intel 865 or later and has embedded SATA interfaces, it should detect SATA devices during startup and display them on the BIOS boot screen. If the drive is not recognized and if you have not already done so, update the BIOS to the latest version. Restart the system and watch the BIOS boot screen to see whether the system recognizes the SATA drive. Run BIOS Setup (usually by pressing Delete or F1 during startup) and select the menu item that allows you to configure ATA devices. If your SATA drive is not listed, you can still use it, but you'll have to provide a driver on diskette during OS installation.
  • Recognition of SATA drives during operating system installation varies with the OS version and the chipset. The original release of Windows 2000 does not detect SATA drives with any chipset. To install Windows 2000 on an SATA drive, watch during the early part of Setup for the prompt to press F6 if you need to install third-party storage drivers. Press F6 when prompted and insert the SATA driver floppy. Windows XP may or may not recognize SATA drives, depending on the chipset the motherboard uses. With recent chipsets e.g., the Intel 865 series and later Windows XP recognizes and uses SATA drives natively. With earlier chipsets e.g., the Intel D845 and earlier Windows XP does not recognize the SATA drive natively, so you will have to press F6 when prompted and provide the SATA driver on floppy. Most recent Linux distributions (those based on the 2.4 kernel or later) recognize SATA drives natively.
  • If the SATA drive is still not recognized, pop the lid and verify that the SATA data and power cables are connected properly. Try removing and reseating the cables and, if necessary, connecting the SATA drive to a different motherboard interface connector. If the drive still isn't accessible, try replacing the SATA data cable. If none of this works, the SATA drive is probably defective.

Problem: The monitor displays BIOS boot text, but the system doesn't boot and displays no error message ¶ 

  • This may be normal behavior. Restart the system and enter BIOS Setup. Choose the menu option to use default CMOS settings, save the changes, exit, and restart the system.
  • If the system doesn't accept keyboard input and you are using a USB keyboard and mouse, temporarily swap in a PS/2 keyboard and mouse. If you are using a PS/2 keyboard and mouse, make sure you haven't connected the keyboard to the mouse port and vice versa.
  • If the system still fails to boot, run BIOS Setup again and verify all settings, particularly CPU speed, FSB speed, and memory timings.
  • If the system hangs with a DMI pool error message, restart the system and run BIOS Setup again. Search the menus for an option to reset the configuration data. Enable that option, save the changes, and restart the system.
  • If you are using an Intel motherboard, power down the system and reset the configuration jumper from the 1-2 (Normal) position to 2-3 (Configure). Restart the system, and BIOS Setup will appear automatically. Choose the option to use default CMOS settings, save the changes, and power down the system. Move the configuration jumper back to the 1-2 position and restart the system. (Actually, we do this routinely any time we build a system around an Intel motherboard. It may not be absolutely required, but we've found that doing this minimizes problems.)
  • If you are still unable to access BIOS Setup, power down the system, disconnect all of the drive data cables and restart the system. If the system displays a Hard Drive Failure or No Boot Device error message, the problem is a defective cable (more likely) or a defective drive. Replace the drive data cable and try again. If the system does not display such an error message, the problem is probably caused by a defective motherboard.

Problem: The monitor displays a Hard Drive Failure or similar error message ¶ 

  • This problem is almost always due to a hardware issue. Verify that the hard drive data cable is connected properly to the drive and the interface and that the drive power cable is connected.
  • Use a different drive data cable and connect the drive to a different power cable.
  • Connect the drive data cable to a different interface.
  • If none of these steps corrects the problem, the most likely cause is a defective drive.

Problem: The monitor displays a No Boot Device, Missing Operating System, or similar error message ¶ 

  • This behavior is normal if you have not yet installed an operating system. Error messages like this generally mean that the drive is physically installed and accessible, but the PC cannot boot because it cannot locate the operating system. Install the operating system.
  • If the drive is inaccessible, verify that all data and power cables are connected properly. If it is a parallel ATA drive, verify that master/slave jumpers are set correctly, and that the drive is connected to the primary interface.
  • If you upgrade your motherboard, but keep your original hard drive (or use a utility such as Norton Ghost to clone your original), your operating system installation may not have the drivers necessary to function with your new hardware. If you're upgrading your motherboard, chances are good that enough things are different that Windows won't be able to boot. You'll need to reinstall Windows.

Problem: The system refuses to boot from the optical drive ¶ 

  • All modern motherboards and optical drives support the El Torito specification, which allows the system to boot from an optical disc. If your new system refuses to boot from a CD, first verify that the CD is bootable. Most, but not all, operating system distribution CDs are bootable. Some OS CDs are not bootable, but have a utility program to generate boot floppies. Check the documentation to verify that the CD is bootable, or try booting the CD in another system.
  • Run CMOS Setup and locate the section where you can define boot sequence. The default sequence is often (1) floppy drive, (2) hard drive, and (3) optical drive. Sometimes, by the time the system has decided that it can't boot from the FDD or hard drive, it "gives up" before attempting to boot from the optical drive. Reset the boot sequence to (1) optical drive and (2) hard drive. We generally leave the system with that boot sequence. Most systems configured this way prompt you to "Press any key to boot from CD" or something similar. If you don't press a key, they then attempt to boot from the hard drive, so make sure to pay attention during the boot sequence and press a key when prompted.
  • Some high-speed optical drives take several seconds to load a CD, spin up, and signal the system that they are ready. In the meantime, the BIOS may have given up on the optical drive and gone on to try other boot devices. If you think this has happened, try pressing the reset button to reboot the system while the optical drive is already spinning and up to speed. If you get a persistent prompt to "press any key to boot from CD," try leaving that prompt up while the optical drive comes up to speed. If that doesn't work, run CMOS Setup and reconfigure the boot sequence to put the FDD first and the optical drive second. (Make sure there's no diskette in the FDD.) You can also try putting other boot device options, such as a Zip drive, network drive, or boot PROM ahead of the optical drive in the boot sequence. The goal is to provide sufficient delay for the optical drive to spin up before the motherboard attempts to boot from it.
  • If none of these steps solves the problem, verify that all data cable and power cable connections are correct, that master/slave jumpers are set correctly, and so on. If the system still fails to boot, replace the optical drive data cable.
  • If the system still fails to boot, disconnect all drives except the primary hard drive and the optical drive. If they are parallel ATA devices, connect the hard drive as the master device on the primary channel and the optical drive as the master device on the secondary channel and restart the system.
  • If that fails to solve the problem, connect both the hard drive and optical drive to the primary ATA interface, with the hard drive as master and the optical drive as slave.
  • If the system still fails to boot, the optical drive is probably defective. Try using a different drive.

Problem: When you first apply power, you hear a continuous high-pitched screech or warble ¶ 

  • The most likely cause is that one of the system fans either has a defective bearing or a wire is contacting the spinning fan. Examine all of the system fans CPU fan, power supply fan, and any supplemental fans to make sure that they haven't been fouled by a wire. Sometimes it's difficult to determine which fan is making the noise. In that case, use a cardboard tube or rolled up piece of paper as a stethoscope to localize the noise. If the fan is fouled, clear the problem. If the fan is not fouled but still noisy, replace the fan.
  • Rarely, a new hard drive may have a manufacturing defect or have been damaged in shipping. If so, the problem is usually obvious from the amount and location of the noise and possibly because the hard drive is vibrating. If necessary, use your cardboard tube stethoscope to localize the noise. If the hard drive is the source, the only alternative is to replace it.

More about Getting Started on Computer Repair

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