SOLUTION FOUND
I had the same problem
I have 2 samsung tabs 1 samssu ng tab 3 model P5210 the other one is samsung tab pro model t520. I thought its the screen issue so i changed the screen gor one of them but same problem a black screen only when i push the power button the side turn back sign light turn on and the other side but nothing on the screen nothing at all, well very simplje open the tablet disconnect all cables remove the battery cables put them back again and it should work . I know it sound simple and easy but thats all .
Good luck