Charge it while it is off, then try turning it on in "Safe Mode" and see if it will start. It will give you limited access, but if it works, then you know there is something that is on the tablet that needs to be removed. Bad app, virus, malware, etc.
To get into "Safe Mode" please do the following.
1. First turn off the tablet.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.