My Sansa Clip + don't react anymore !!!

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?