Try shutting it down and then starting the tablet up in "Safe Mode". If it loads, then there is probably something, a bad app, virus, malware, etc., on the device that you will need to remove to get it to work correctly. If, however, it still won't load in "Safe Mode" then you may have to either do a "Hard Reset" of the device, or have it looked at for any hardware problems.
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.