Here are a few suggestions:
1. Try pushing the power button and holding it until it resets itself.
2. Push a paper clip end into the hole in the back while holding the power button.
3. Plug it in for an hour, then pull the USB without ejecting. (I hardly ever eject, but in your case, what could it hurt?)
4. Like Rumpelteazer said above, try charging it for 4 hours on an "active" computer without it going to screensaver or sleep mode. (People advocate the wall charger, but I've never bought one.) Here's the thing, after 2 hrs, pull the plug, let it settle itself, then replug it for the next 2 hrs. Works for me.
Good luck and be sure to let us know how this turns out.