Try starting it up in "Safe Mode". If it will fully load, you won't have access to many things, but that will also tell you that the problem is probably not hardware. You should then check the device for bad apps, malware, viruses, etc. and once you remove anything that shouldn't be there, restart the device.
Should it still not work, you may have to do a "Hard Reset" but I would save that as a last resort, as it will wipe all personal data.
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.