I have a ipod sad face. gets into disk mode but back to sad face

ok this is really frustrating. i got a sad face on my ipod 4th generation 20gb classic. i did the infamous resetting shtick which you hold the menu and select buttons and then the select button and play/pause. it got into disk mode. however when i connect it to the computer it detects it and then diskmode goes off again and the steady battery icon pops up and the computer automatically loses detection. i dont think its the battery becuase i charged until it said full while in disk mode. what can be the problem here? anyone?
thanks.