It can't work the screens

Sounds like the OLED panel was either damaged or just failed. I see that from time to time in my shop. You can start by reconnecting the display connector on the board. If that doesn’t fix it, you’ll need to order a replacement screen. I recommend buying one that is preinstalled on the frame that way there’s less of a chance at breaking the replacement screen. All you’ll have to do is transfer the internals like the board and battery. If you just need the data you can try to source a donor phone that’s locked and take the screen from that. Just make sure your transfer the charge port from your phone to the new one. Not all of the ports in the S8 lineup are a “one size fits all” type of deal.