I bought Garry's Mod on Steam and when I launch the game it loads for a few seconds and then crashes to the desktop.  I do not know why this is happening since my computer can run Counter-Strike Source and Day of Defeat Source just fine.  Has anyone else had this happen to them?

Right click it in games tab > Properties> Local game files> then verify the game files/ integrity of cache or whatever it's called.

I just tried that and it still just crashes to the desktop.  I have also reinstalled it three times and nothing seems to be working.