How do I power off to factory reset after I forgot password,like?

This is a Samsung tab4 I got from a friend. His password is 4 numbers, like a pin, bit now it won't accept it. I must have hanged it and forgotten.

So I realize I must do a hard reset which starts with the tablet OFF.

I cannot turn it off. If I let it run out of battery I fearnit will Uber its state and be the same as soon as I plug it in.

I would appreciate any wisdom.I already checked around and got nowhere, so far.

Yes I did push all three buttons and held them over 30 secs. The screen turned Black, then I touched something and it was right back at the sign in screen, so fast it had never gone off.

Thank you.