Try turning it off and starting in "Safe Mode". If it will load, while access will be limited, it will tell you there is a problem on the device. Bad app, bad update, malware, virus, etc. that you need to remove to fix the problem. If it still won't start, even in "Safe Mode", then I would have it looked at.
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.