Turn it off and then try turning it on in "Safe Mode" and see if it will load. If it will, then you likely have a virus, malware, bad app, etc., on the device that you need to remove. However, if it won't even start up in "Safe Mode" then a "Hard Reset" (which will wipe the device) or possibly even a hardware repair will be required.
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.