Garry's Mod doesn't launch

I’ve played it before, but I formatted my HDD and decided to try playing it again. The little steam Window pops that tells me “Launching Garry’s Mod” but then it just goes away and nothing happens.

The process just ends itself. It doesn’t give me any error messages or anything.

Any ideas Facepunch?

System specs.

Athlon II X2 @ 3.4GHz
4870 512MB
2GBs DDR2 800MHz
Windows 7 Professional 64-bit
80GB HDD with OS and 250GB storage.

Download gmod 2010 from torrents.

(User was banned for this post ("Suggesting warez" - Craptasket))

Try adding “-fullscreen” to launch options.