Try turning it off and then starting up in "Safe Mode". If it will load in "Safe Mode" then you may well have something on it that shouldn't be. Bad app, virus, malware, etc.
If, however, it still won't start up in "Safe Mode", then you may have to do a "Hard Reset", if it software related, or have it repaired, if it is hardware related.
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...