[HELP] Bug loading screen

Hi everyone !

I explain my problem.

There are about 3 days I buy Garry’s mod, so I started the installation on Steam, so far no problem.

Problems then arrives. When I run the game, the game starts, there is a blue screen with the logo “loading” at the bottom right of the screen, then after 1 ~ 5 seconds, nothing more, the processus is killed(hl2.exe). And there is no error message, it’s a clean cut.

I managed to get the error message one time, I took a screenshot of the top of the message, where he had the information needed. But since then I have not had this message as cuts without messages.
Error message : http://www.hostingpics.net/viewer.php?id=260528Sanstitre.png
Behind the message you can see the loading screen.

So I looked on some forum, but nothing worked.

What I’ve tried :

-Disable Steam Cloud for Gmod ==> Doesn’t work
-Uninstalled and reinstalled 2 times, Once normally and once by removing the file directly ==> Doesn’t work
-Verify integrity cache on all my source games(CS:S, Day of Defeat etc…) and Gmod too ==> Doesn’t work.
-In launch option, I tried to write : dxlevel 80/81/85/90/91/95/8/9, -autoconfig ==> Doesn’t work.
-Launch in admin mode ==> Doesn’t work.
-Launch steam in english ==> Doesn’t work.
-I updated my drivers and DirectX ==> Doesn’t work.
-Disable Antivirus/Firewall ==> Doesn’t work.

I would also like to clarify that I have no addon, the game is new.

I have no idea to fix the problem, so I come here for help.
I have a fucking bad connection(2M),I am so tired uninstalled/reinstalled all these games.

Thank you in advance to those who try to help me.