Hello and welcome to justanswer, My name is ***** ***** i will be assisting you today,
I'm sorry about the issue, please Try hard reset, turn off your device and hold power button + volume up key then wait for a few seconds, navigate it using the vol down and up button and select restore or reset device.
power button to accept / ok
Note : all of the files on your tablet will be erased and will restore to a state of factory device
let me know the results please