Go to your Library on Steam, right click Garry's Mod, click 'Properties' and set launch options.

Put this as a launch option:

Then start Garry's Mod again, should fix it.

Go to your Library on Steam, right click Garry's Mod, click 'Properties' and set launch options. Put this as a launch option: [code]-dxlevel 95[/code] Then start Garry's Mod again, should fix it.