Try starting it up in "Safe Mode" (instructions below) and see if it loads. If it does, then you need to check the device for malware, viruses, bad apps, etc. Remove the problem once found and then restart the tablet to get out of "Safe Mode". If it won't even start in "Safe Mode" then you are looking at either a "Hard Reset" (which will wipe all data) or having a tech look at it for possible 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 repeat the steps above, and you should see "Safe Mode: OFF" rather than on.