Try booting your device into “Safe Mode” and performing a factory reset. Keep in mind that this will erase all your saved files (so back them up to a removable storage device), but it may also fix the problem.
# Turn on the tablet.
# Press and hold down the Power button until the Power Menu appears. This menu should have an option to Restart the tablet.
# Press and hold down the Restart option until a message appears asking if you would like to boot into Safe Mode. Select OK.
# When the table boots into Safe Mode, go into the Settings app and look for the '''Factory Reset''' option. This will erase all the data on your tablet and reinstall the operating system, giving you a fresh start.