Try seeing if it will load in "Safe Mode". If it does, while it will have restricted access, you will then know something is on the device that is the cause of the problem. Bad app(s), virus, malware, bad update(s), etc. You will then need to remove the cause and restart the tablet.
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.