Try starting it up in "Safe Mode" and see if it will load. If it does, then you likely have something on the tablet that needs to be removed. Bad app, virus, malware, etc. If, however, it doesn't start up even in "Safe Mode" then you may wish to try a "Hard Reset", just remember that will totally wipe the device and restart it like originally (before you put anything on it) was. That is if it will do the reset. The final option would be to have a tech look at it.
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...