Try starting up in "Safe Mode" and see if it will fully load. If it does, you will have limited access, but then you also know there is probably something on the device that is causing the issue. Bad app, virus, malware, etc. That you will have to remove to get it to work correctly. However, if it won't start up even in "Safe Mode" then I would 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...