You can try this...
To do a "Factory Reset" (which can delete some data)...
1. Locate the pinhole on the tablet. It is usually on the edge, or near the SD card and SIM card slots.
2. Depress the pinhole with something tiny (But not sharp! Don't want to damage it.).
3. The device should restart.
If you don't want to risk losing any data, then your other option is to wait for the tablet to lose power completely and then it will turn itself off.
I would also suggest, once the tablet has lost all power and turned off, that charge it, while it is turned off, and then start it in "Safe Mode". This would help you get it working, without any side apps loading, and allow you to remove anything you need to remove that is messing with the device, safely, and then reboot the tablet.
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.