Cannot display this video mode

I was running GMOD in windowed mode and I decided to change it back to full screen, but when I did I got a black screen with ‘Cannot display this video mode’. When this message comes up I cannot do anything as Ctrl+Alt+Delete does not do anything. This has happened on startup the last couple of times that I have tried to run GMOD. I have a ATI 2400HD video card and GMOD worked fine up until then. Is there a way to access the video settings of GMOD from somewhere else and what else can I do?

Right click GMod in steam games list

Click properties

Click “set advanced launch options”

Type “-autoconfig” in the box (without quotes)

This will reset all your resolution and stuff

okay thanks for the help, i can now play gmod again