Start by shutting it down , If you cant shut it down normally try holding the power button down until it does shut down if this doesnt work you will need to either let the battery die or disconnect the battery. Heres a guild to help with the battery.
Android Tablet Nobis NB09 Battery Replacement
Once you have the tablet shut down we want to restart in the android screen we get there bypressing the reset button on the back with some sort of pin then holding down the power button and the volume button together until you see the android man . From here we can do a factory reset. follow the instructions from this instructional video
remember though when you do a factory reset you loose everything on the tablet , all photos , music, contacts it goes back to the settings it had when new. This is a trouble shooting guild it may also be helpfull
Nobis NB09 Troubleshooting