Try starting it up in "Safe Mode" and see if it will load then. If it does, then there is something on the device that needs removing. Bad app, malware, virus, etc. Once removed it should then work. If, however, it won't start up even in "Safe Mode" then you are looking at either a "Hard Reset", which will wipe the device and start it over without all the changes or your stuff, or take it to a tech to check 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...