Gmod crashes when I start it.

[hhjer1]

hey,
since a couple of day, I can't launch gmod anymore. When I start it, it gives me a black screen, and when I use alt-tab, I see the error:

Can't find background image
'materials/console/background01_widescreen.vtf

I validated the game, and team fortress 2, but it didn't work. I reinstalled the game twice but that also didn't work. I hope you know a solution because I really would love to play gmod.
Pc specs:
i5 4e gen
gtx 960
8gb ram
1 tb hard disk
msi motherboard
1 monitor.

[hhjer1]

anybody who can help me?

[Desasterx3]

Try reinstalling css, seems to be related to counterstrike from what i found on google.