You might want to see if the battery connector is actually completely connected. You would have to, "very carefully" take the back of the Tablet and see if the battery connector is fully attached. If it is partially off "very gently" press it back in and this should resolve the problem.
If this doesn't do it, then you would have to try a "Hard Reset" of the device.
NOTE: Doing this will clear the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the tablet.
To "Hard Reset" the tablet...
1. Make sure that the Samsung tablet is actually powered off.
2. Press the "Power" and the "Volume Up" buttons, together, until you see the start-up logo on the...