1st gen Shuffle suddenly not taking charge, not recognized

1st gen Shuffle. I only use it at the gym, so sits in my gym bag. Was away from gym for 3 months with an injury so shuffle sat in there un-played, without being charged up. When I went back a few weeks ago, the shuffle still had juice and played. The next time I went to the gym I plugged it into USB car charger to charge it way to gym as usual and when I went to use it, nothing. No music and no light on the battery indicator - neither amber nor green. I plugged it back into the car charger - still nothing. Then plugged it into computer and it doesn't show up on the desktop, system profiler or iTunes.
I've never timed it, but I would guess the battery up to now has lasted 4-5 hours per charge.
Any thoughts on what to do?