Hi,
What is the model number of the tablet?
Have you tried pressing the ''reset'' button for about 5-10 seconds, to see if this resets the tablet back to normal?
It is found on the back of a lot of Ematic android tablets
You will need a pin or opened paperclip to operate the button as it is recessed in a hole in the back cover.
Do not confuse the hole with the microphone inlet hole. You may damage the microphone if you shove a pin in there.
Check the tablet’s layout description in the User Guide that should have come with the tablet to help verify the reset button’s location, (if it has one that is).