Try resetting your tablet.
Resetting your tablet will erase all your User data and downloaded apps. It will restore it to a factory default condition. It will be like when you first bought it.
Be sure that the battery is fully charged before you perform a reset. Do no leave the charger connected when you perform a reset. Remove the external SD Card (if any installed).
Here is a link that shows how to perform the reset. There is a comment at the bottom of the page that you may wish to be aware of if the first procedure doesn't work for you also.
Be patient a reset takes a little while to complete.