Ipod touch wont connect to pc

Hello,

my ipod touch 1st gen wont connect to my pc..........so l=when i connect it to the computer via usb it doent do anything i mean like it wont charge it wont sync it wont show on my computer or itunes.........its like its not connected at all but when i charge it with a wall charger it works nd when i try to charge it when it has no battery on the pc it works but it stops charging as soon as its on again

win 7....

help!!!! plz