iPod Nano isnt reconsized by My Computer and iTunes.Still Charges,HELP ME!

My iPod 8gb 4th Genoration Nano wont sync. It doesnt appeer in My Computer and iTunes but it still charges. When it works, it says 'iPod cant sync' or if i try and restore it it says 'iPod cant restore'. Some times it says 'This USB device is not reconised'. Sometimes it works. I have tried to restore it and restart it.

PLEASE HELP!