It sounds like, from what Arya said, the USB port and the part that goes in it aren't getting good connection. If this IS the case, you can always try and put the terminals (the little metal things in the part that plugs into the USB port) back to where they were. If you are going to do this a: I take no responsiblity if something messes up and b: you might want to look at the end of a properly-working USB device to see where the terminals go.
Hope this helps,
Racr.