Bear with me, if these have been tried, but at least you didn't say that you have tried everything.
iPod Not recognised by Windows
- If you are using Windows, I would suggest reinstalling iTunes, this would repair any corrupted Apple Mobile Device driver that is required for iTunes to interface with USB devices.
- After Re-installing, reboot your PC.
- Disconnect the PC from Internet
- Stop your Antivirus
- Reset your iPod - Press Menu and Center Button for about 10 secs till the Apple logo comes ON then release the buttons. Select you language.
- Connect your iPod to a high power USB 2.0 Port and not to any USB hub. (if you using a Mac, not on the Keyboard USB port)
- What do you see on the iPod Display - should be sychonisation for a few secs then do not disconnect screen.
- if iTunes comes up restore it.
- After restore - Start back your antivirus and connect the Internet.
If this doesn't work, refer to this link on do a disk diagnostic by tt2 to chack the health of your hardisk.
if you hardisk is still healthy then do reformat your Hardisk.
Have a nice day!