I thought I would share this quick fix with you all who are having the same problem. If your Sansa Clip will not charge with the USB, most of the time a firmware update will solve the problem. However, my battery was so low that as soon as I powered it on to update the firmware, it would immediately shut off.
As soon as you power on the Sansa Clip, wait for it to say “Updating Firmware.” Immediately plug the USB cable into the Clip before it goes to the “Battery Low” shutting down message. Plugging in the Sansa Clip at this exact time will not interrupt the Sansa Clip from updating its firmware, and will not go into PC Connection mode.
I read some others having the same problem awhile back and didn’t see a fix, in fact some of the people just RMAd. This solved my problem. I have a 2gb btw. Hope this helps some. Good day!