it could be because you are either having a driver conflict error as detailed in the apple help page:-
http://support.apple.com/kb/TS1538 for driver errors andÂ*http://support.apple.com/kb/TS1369 for USB power issues
or more likely its a USB power issue. if its a Acer, Asus,Compaq, Dell or Packard Bell or LAPTOP then is 99% likley due to it having low spec 100mA usb ports instead of full spec 500mA ones.. Make sure you have a full power USB connection (many laptops and keyboard connectors only give 100mA max rather than the full 500mA, also do not connect via an unpowered hub either as this only PARTLY charges the ipod
connect it direct to the computer on a full power USB port or via a powered hub (mains transformer connected to it) and it should be OK.
Leave it charging on this for at least an hour before proceeding further.
make sure you have the latest itunes 8.2.0 or 9.0 (downloaded on your PC from www.apple.com/itunes/download then restart PC first)
and reset the ipod before connection (menu and centre key till screen blanks then connect once it lights up).
the say YES to the 'pair with this computer' Message
if after doing the USB power check you still have problems you need to call apple for a swap for replacement... as batteries can be killed by improper usage apple has a page at http://support.apple.com/kb/HT1726 that tells you how to get the most from your battery