Hi,
Try performing a factory reset on your tablet.
''Be aware that a factory reset will erase all your user data and downloaded apps. It will restore your tablet to a factory default condition. It will be like when you first bought it.''
Before you perform a factory reset:
Ensure that the battery is charged.
Do not leave the charger plugged in when you perform a reset.
Remove the external SD Card (if any installed)
Here is a link that shows how to perform a factory reset.
https://www.youtube.com/watch?v=QoiLEpT3E4o
Be patient, it takes a little while for the reset to complete.