If a sad iPod icon or an exclamation point and folder icon appears on your iPod’s screen, or with sounds of clicking or HD whirring, it is usually the sign of a hard drive problem. Make sure you do all the following “TRYs”
A. Try to wait 30 minutes while iPod is charging.
B. Try another FireWire or USB through Dock Connector cable.
C. Try another FireWire or USB port on your computer .
D. Try to disconnect all devices from your computer's FireWire and USB ports.
E. Try to download and install the latest version of iPod software and iTunes
B. Still can’t see your iPod, put it in Disk Mode and connect with a computer, instead of doing a Restore on iPod Updater. Go and format the iPod instead.
For Mac computer
1. Open the disk utility, hope your iPod appears there (left hand side), highlight it
2. Go to Tab “Partition”, click either “Delete” or “Partition”, if fails, skip this step and go to 3
3. Go to Tab “Erase” , choose Volume Format as “MAC OS Extended (Journaled), and click Erase, again if fails, skip it and go to 4
4. Same as step 3, but open the “Security Options....” and choose “Zero Out Data” before click Erase. It will take 1 to 2 hours to complete.
5. Eject your iPod and do a Reset
6. Open the iTunes 7 and click “Restore”
Diagnostic mode solution
If you have tried trouble shooting your iPod to no avail after all the steps above, chances are your iPod has a hardware problem. The iPod's built-in Diagnostic Mode is a quick and easy way to determine if you have a "bad" iPod.
You need to restart your iPod before putting it into Diagnostic Mode. Check that your hold switch is off by sliding the switch away from the headphone jack. Toggle it on and off to be safe.
Press and hold the following combination of buttons simultaneously for approximately 10 seconds to reset the iPod.
iPod 4G+ (includes Photo, Nano, Video, and Mini): "Back" and "Select"
You will hear an audible chirp sound (3G models and higher) and the Apple logo should appear backwards. You are now in Diagnostic Mode. Navigate the list of tests using "REW" and "FFW". The scroll wheel will not function while in diagnostic mode.
Bottom line here is that this might help you to narrow down the fault finding. Hard drives for the iPod a readily available and easy to change. Just remember that you most likely will lose your files from the iPod. Good Luck.