Hi. You will need to reset your Galaxy Tab 3 at this stage. Do the following to reset it. Power it off, and the proceed to hold both the Volume Up + Power + Home buttons at the same time. Release them when you see the Samsung logo. A recovery menu should display. Scroll to 'Wipe data/factory reset' using the Volume down key and confirm selection by short pressing the Power button. Again scroll to 'Yes---delete all user data' and confirm with the Power button. Short press the power button again to reboot the phone when the wiping is completed.