It could be the tablet is going bad and either needs to be "Hard Reset" or has a hardware problem. It could also be that there is a virus, malware or bad app on the it that needs to be removed.
If you can, I would save anything you want from it to a computer or cloud account and then do the "Hard Reset". If that doesn't resolve the problem, then I would have a tech look at it.
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually...