Plug it in to your pc, let it charge even if it says its not for 30mins.
Then do the basic reset thing that turns it off properly, then when its loading and reaches the full bar, when the screen goes black for a brief second do the master reset (back +up). I did this with my zune after it lost most of its power, then i dropped it and it wouldnt turn on. After i had done this, it asked me to plug into the pc, so i plugged it in, and it refirmware my zune as i think it had been corrupted.
Hope dat helps.