It sounds like you have something on the table that is preventing it from turning off. Bad app, malware, virus, etc. Try turning on the tablet in "Safe Mode" and see if it will then let you turn it off. If it does, then you need to scan the tablet for the problem and remove it.
Should this all not help, you may have to do a "Hard Reset" on 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...