I assume you've tried the usual...
- Hold power down for 15 seconds
- Try a different charger and cable
If that hasn't worked, you could try holding down BOTH
back and forward (next/previous) page buttons then
pressing power on button.
Still not working AND no longer under warranty?
You could open the device up to physically disconnect the battery from the motherboard and leave it disconnected for a while, before reconnecting and trying again. Obviously you're proceeding at your own risk here!