Gmod White/Blackscreen

My computer is running fine now.
But whenever I afk and leave the game open. The PC would tend to Sleep and the monitor display would turn off.

When I go back and turn it on, I am still in the server where I play in but Gmod seems to be black screen or white. I can still hear the sounds in the game.

I turned off the sleep mode of my PC, but when I go afk I close my monitor through its power button to save power.
But when I came back and turn the Monitor back on. The Game is back to either white or black screen, and still hear the sounds in the game when I move around.

Is there any solution to this without closing the game?
Is there any shortcut keys to make Gmod Fullscreen like in Windows XP?
I’m using Windows 7.

I was thinking maybe if I switch to fullscreen from window, the black screen will vanish. But since I cant see, then I can navigate to the options.
And I didn’t want to close the game cause I would lose the chat logs from the game that I missed while I was gone.