lilianagonzalez84, here is what Apple suggest. I could not post it as a comment since it would lose the layout and it would be almost impossible to decipher ;-) sorry about that.
Power but No start up
• No startup chime, some video activity, Apple logo, startup spin dial
• Startup chime with possible beep tones.
• Fan, hard drive spin or optical drive reset sound
• Sleep LED is on , blinking or went out
• Caps Lock LED toggles when pressed
1. Reset SMC.
2. Verify startup process passes initial memory checks – no beep errors or flashing sleep LED
indicators. Display activity is starting up.
3. Clear PRAM. Verify starts up from user drive.
4. Connect known-good external bootable device and press Alt key during startup then select
external startup device to bring up system for diagnostics.
5. Verify presence and status of user hard drive. Use Disk Utility to repair drive and file permissions.
1. Reset SMC and Clear PRAM to set default startup device to internal hard disk drive (HDD).
Yes User hard drive bootable,issue resolved default settings.
No Customer system not starting up, go to step 2
2. Is system indicating a memory error with repeated sleep LED 1 or 3 flash sequence and beep
tones if sound is enabled?
Yes Troubleshoot memory issues,go to step 3
No Continue with startup sequence verification go to step 4
3. Reseat customer memory and/or swap in known good memory to isolate bad memory and replace defective parts.
Yes Customer memory defective and replaced. Continue to verify startup process. Go to step 4
No Should known-good memory fail in one or more slots,replace logic board.
4. Hold the Alt (Option) key during startup and verify there is a bootable hard drive shown in Startup Manager. Choose customer hard drive. Does start up from this drive work?
Yes System starting up from customer hard drive. Startup issue resolved
No Customer hard drive not present or does not start up from this drive. Continue to find bootable device. Go to step 5
5. Insert product OS install disc in optical drive. Install disc is bootable and should be present in Startup Manager. Can system start up from OS install disc?
Yes Starts up from optical drive - customer hard drive not yet bootable, go to step 8
No Computer has no internal bootable devices. Test external startup devices, go to step 6
6. Boot from a known-good bootable copy of product OS on a USB drive or network server to start up and verify internal mass storage devices are available using System Profiler and Disk utility.
Yes System started up from external device and reports data regarding internal SATA devices. Go to step 7
No No startup devices available. Replace logic board
7. Troubleshoot optical drive and optical drive cable with cable reseat and knowngood part substitutions. Is there a defective optical drive component to replace?
Yes Cable reseat solved issue. Continue to verify hard drive issues, go to step 8.
Defective optical drive cable found and replaced. Continue to verify hard drive issues, go
to step 8.
Defective optical drive found and replaced. Continue to verify hard drive issues, go to step 8
No Replace logic board.
8. Use Disk Utility loaded from OS install disc to verify if hard drive is available on device list. Is customer hard drive listed in Disk Utility?
Yes Customer hard drive available for inspections and repair. Go to step 10.
No Hard drive not present, troubleshoot hard drive and cable. Go to step 9.
9. Troubleshoot hard drive and hard drive SATA cable with cable reseat and known-good part substitutions. If customer hard drive, is there a defective hard drive component to replace?
Yes Reseat of SATA cable now has customer hard drive visible in Disk Utility, go to step 10
Defective hard drive SATA cable found and replaced,now has customer hard drive visible in Disk Utility, go to step 10
Suspect customer hard drive defective, attempt OS restore,go to step 10.
10. Boot system with Shift key down. Does it work?
Yes Go to software troubleshooting article
No Go to step 11.
11. Use Disk Utility to repaircustomer hard drive and repair permissions if system OS found on hard drive. Is hard drive bootable after software repairs?
Yes OS on customer hard drive repaired, issue resolved.
No Hard drive not bootable, perhaps missing OS, go to step 12
12. Use Disk Utility to partition customer hard drive with one GUID partition then restore Mac OS from product OS install disc. Is hard drive bootable after OS install?
Yes Customer hard drive now starts up from new OS image, issue resolved
No Replace hard drive."
So if what mayer suggest does not work for you, you may give this a try.