You will need to try a full factory reset.
If possible, back up all of your data first if you haven't already done so.
Let me know if that works?
Press and hold the Volume down, Volume up and Power buttons until the Samsung logo appears on the screen. Scroll to wipe data/factory reset by pressing the Volume down button. Scroll to Yes -- delete all user data by pressing the Volume down button. The tablet will reset and wipe all contents.
Ok, so you cannot get any Samsung logo at all on the tablet?
Ok, then unfortunately the tablet is bricked, and will need to be returned to a Samsung service center fore any possibility of recovery.
Yes, unfortunately that means it is beyond repair.