Try starting it up in "Safe Mode" and see if you can get it to load. While it will be limited in function in that mode, then you will know also that it is software and not hardware related. So then I would check the device for bad apps, viruses, malware, etc.
If, however, it still won't load in "Safe Mode" then it is likely hardware and you need to contact the manufacturer (if it is under warranty) or a local tech to see about fixing 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 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.