Remove the battery and leave for a few minutes. Keep the battery out but plug in the power supply, preferably a wall supply. Wait a few minutes again then press and hold the reset button for over 10 seconds. If this works, replace the battery and charge.
Another option is to try and update the firmware. If you do this, make sure you have the power supply plugged in.
Last edited by Stormchild; 08-17-2011 at 06:15 PM.