when i start garrys mod it prepares it just fine… but with it goes to open gmod in a window or full screen it just closes out. i dont understand this problem maybe some1 with a little bit more of a brain could help me out with this problem… please help me… i made a video of it on youtube if the text is not so clear… here is the link: http://www.youtube.com/watch?v=JjorAVGs200
Uninstall AdvancedSystemcare . I had a similar problem. Not sure if same.
You have no source games installed.
Install Team Fortress 2, run it, exit, then launch GMod.
You need at least one Source game installed to play GMod. You have TF2 registered to your account, but it isn’t installed. Download and install it, run it, exit, and then run GMod.