Try starting it up in "Safe Mode" and see if it will load. If it will the problem then is likely software related. Virus, malware, bad app, etc. that would need to be removed. If, however, it won't start up in "Safe Mode" either, then you may need to either "Hard Reset" the tablet or have it looked at for 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"...