I have the same problem with a Clip I purchased about 8 months ago. I returned it to the seller and they said it was fine and returned it to me. It WAS fine, but then the problem occurred. When I plug the USB in, the computer doesn’t recognise anything is attached - it doesn’t come up in the ‘My Computer’ list, if that makes sense.
I’ve tried holding down the power button for a few minutes but nothing happens. Any other suggestions?