You could try starting it up in "Safe Mode" and see if it will fully load. If it does, while you will have limited access, you will also know that there is something on the device causing it to not work. Bad app, virus, malware, etc. If that is the case you will need to remove the problem and then reboot. If that doesn't work, the you may have to either do a "Hard Reset" or it is a hardware problem.
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.