Computer not recognizing my iPod

Any single action or combo may help

Restart your iPod. Hold down the sleep and home keys until you see the silver apple. Let it reboot and try again.

Reboot your computer.

Swap out the USB port you're using

Swap out the cable if you have another one

See if iTunes is up to date. If not, update it and try again.

Uninstall and reinstall itunes.

See:

iOS: Device not recognized in iTunes for Windows

I would start with

Removing and reinstalling iTunes, QuickTime, and other software components for Windows Vista or Windows 7

or

Removing and Reinstalling iTunes, QuickTime, and other software components for Windows XP

Run this to help if it identifies the cause

iTunes for Windows: Device Sync Tests

Have you tried on another computer to help determine if you have a computer or iPod problem?