Try starting it up in "Safe Mode" and see if will load. While it will have limited access, if it does start up, then you know there is something on the device that is the problem. Bad app, virus, malware, etc. that you will need to remove. If it still won't start up, then you may need to "Hard Reset" the device, or it may well be a hardware issue.
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...