You may have to wait until it loses power (unless you wish to try pulling the battery, which would be unwise if the tablet is under any warranty). Once it is out of power, let it charge while off and then start it up in "Safe Mode". It will give restricted access and should allow you to uninstall any app(s) that are the cause of the issue, or remove any malware or viruses while as well. Once you have removed the problem, you can then restart the device out of "Safe Mode".
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.