I have this Samsung S7 Edge. Phone worked fine. Then I placed it in box. After 4 months I decided to use it again. Of course battery was empty. I charged it a bit, and it would not go past the Samsung logo screen.
I have tried all things that I found on internet, like resetting it, and clearing cache but it did not fix the problem.
I took it to service, and after couple of days I got reply that the flashing did not fix the issue. Service man said that one of the chip is bad, and that is the reason it does not boot up. Also he said it is known problem with S7 phones. Fixing it is more expensive then to get another S7.
I do know hardware failure can prevent the boot, and many other things. I am wondering at the statement 'It is known problem to S7 phones'. If he is not telling the truth, I would rather try with another repair shop, before throwing the phone away.