Well, you could try a "Hard Reset" but that will completely wipe the tablet of all your personal data. Try starting with loading in "Safe Mode" and see if this will work. If it doesn't, then I would try the "Hard Reset".
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.
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not...