Help!Ipod Touch!

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?

Make an appointment at the Genius Bar of an Apple store.

Apple Retail Store - Genius Bar