Do a soft re-boot, hold the power button down, at the same time hold down the minus side of the volume button, about 15 to 20 secs it should then re-boot, has worked for me several times. Hope this helps.
I've just has the same problem and got a fix. The tablet had been on the charger for a couple of hours so I knew it should have been charged. Tried holding the power button and volume button down for 10 sec but with no result so I then re-connected the tablet to the charger and tried it again. After about 14 or 15 seconds the battery charging indicator came on and showed that the battery was 99% charged. I then hit the power button and the tablet came on after about 7 or 8 seconds. It seems that you need to have the tablet connected up to the charger for the power/volume solution to work, Hope this works for you .....
beemer1100