Another Noob Question

[Regulus77]

Hello. When I have to AFK longer than a few minutes, I come back to a dark screen and I can't see. I can hear the game sounds but the screen has gone dark. I have been having to restart my PC and log back in to resume play. Is there a reason that this happens or is there a setting that can be changed so this doesn't happen or is there a key or combination of keys to push so I can make that dark screen go away?

Thanks in advance.