If you tried the instructions I am including below (for a "Hard Reset") and it won't work, I have to ask if the device was rooted? If it was, then nothing will work to restore it until it is unrooted. If it wasn't, then it may well be a hardware issue.
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press the "Power" and the "Volume Up" buttons, together...