So you turned off the device and tried a "Hard Reset"? Did you do the following?...
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually powered off.
2. Press the "Power" and the "Volume Up" buttons, together, until you see the start-up logo on the screen.
3. Once you can see the logo, release the buttons and allow the device to enter the "System Recovery Mode".
4. Next use "Volume Down" button to get to the "wipe data/factory reset" option When in recovery mode the "Volume Up" and "Volume Down" buttons are how to can navigate and highlight what option you need.
5. Once you have selected the "wipe data/factory reset", press the "Power" button to select that option.
6. On the following screen, repeatedly press the "Volume Down" button until the "Yes - delete all user data" option is what is selected.
7. Then press the "Power" button to hard reset the tablet.
Also, you can try the following....
1. While on Samsung logo. press power key + volume up and down + home button (all together)
2. When the screen is off. Press Power key + Volume Up + home button to enter recovery mode.
3. Wipe Data
4. Wipe Cache
5. Reboot to system
Let me know if either works for you.