When I double-click it in steam, the “Preparing to launch garrysmod” window appears for about 5 seconds, then a screen flashes like it was about to launch but then nothing…The screen just vanishes. It just started happening out of the blue a few hours ago…any ideas?
try deleting local content. if that doesnt work then do -dxlevel 70 if that works but all you get is a black screen just let it sit there at the black screen it will take a while to load up if its the first time.
A combination of
-dxlevel 90 -fullscreen
in launch options worked great, thanks for the help!