I dont know how to put in to words... HELP!

Hey guys just recently today since an hour ago I get this awful error. I will be playing in an online server and in about 20 minutes everytime my whole scren wants to fuck up:

I havent downloaded anyhting please help me!

Vanilla Gmod perhaps?

[editline]12:31PM[/editline]

Or if that doesn’t work, I recommend a reinstall.

Vanilla gmod?

And I tried reinstalling sadly the same thing occurs :./

oaoh.jpg i dont know.

If it helps that little weird square at the bottom right is there no matter what on multiplayer.