Gmod crashes during startup "hl2.exe has stopped working"

So I bought this game on Dec. 24th and it crashes every time its starting up. On the bluescreen where the Facepunch logo is. I have a youtube video showing you my problem here

Ive tried the “-dxlevel 81”
Ive reinstalled Gmod 20 times
Ive reinstalled TF2
Ive reinstalled CSS
Ive verified integrity of game cache on all of them
Ive tried the hotfix where you open up 2 Gmods but steam wont let me open up 2 at the same time.
Ive updated ALL of my drivers
Ive updated ALL of my hl2 games (CSS, TF2, Gmod)
Ive reinstalled Steam
Ive defragmented the game files

Please send me a message on anything if you can help me!

12/30/12 EDIT - Did a factory reset on my computer, getting rid of a lot of sh!t, and it also fixed my game. No more errors! Also it only took me about 3 hours total to get all my files back and my computer and everything. Runs much better now too. If youre having these same problems, they probobly are from different random reasons, so best of luck on your troubleshooting!