Try starting it up in "Safe Mode". If it will load, even though you will have limitations to your access, this will let you know that there is probably something on the device. Bad app, virus, malware, etc., that needs to be removed. Once removed, then you should be able to use the device normally.
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.