Try turning it off and then start it up in "Safe Mode" and see if it will load. If it does, you may have something on the device (bad app, virus, malware, etc.) that is why and you would have to remove said items to get it to work right.
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.