Try starting up in "Safe Mode" and see if it will load. If it does, while you will have limited access, you will then know there is something on the device causing the problem. Bad app, bad update, virus, malware, etc. Once you remove the issue then you can start the tablet out of "Safe Mode". Now if it won't even start up in "Safe Mode" then you may have to consider either a "Hard Reset" of the device, or have it looked at for hardware issues.
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.