Try this and see if it will let you get into the tablet.
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.
Once in "Safe Mode", if the problem does not persist, then you have something on the tablet that needs removing (app, malware, etc.,). You will have to remove the problem for it to work correctly again.