Try turning it on in "Safe Mode" and see if it will load. All things won't run in that mode, but if it will start up, then you need to check the tablet for viruses, malware, bad apps etc. Once you have remove the problem then restart the tablet again.
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.