Try starting it up in "Safe Mode" and see if it will start up. If it will, you probably have a bad app, malware, virus, etc., on the device that needs to be removed. If it won't start up in "Safe Mode" either, then you may have to do a "Hard Reset" however I would save that as a last resort as it will wipe all your personal data.
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...