I'm stuck on the "Preparing to launch Garry's Mod" window

[Skerious]

Every time I try to play GMod, Steam ends up being stuck on the "Preparing to launch Garry's Mod" window, and it doesn't seem to actually launch it at all. What's the problem, and if I can, how do I fix this?

[Charlievrw]

Same thing is happening for me.

[foobz]

Same here.
I've already tried the -dxlevel90 trick in the launch options, and it hasn't worked since the update.
I'm running Vista on a 2 year old HP Pavilion dv5 laptop, if that helps.

[Skerious]

I should mention that Gmod works fine now. I'm not sure what the problem was, and it seems like GMod just randomly decided to work again, so hooray, I guess.