HL2.EXE stopped working

I seriously do not know how to fix this problem anymore. I tried so many different ways that I feel as if my only hope of this problem to go away is if I get Window 7.

I tried the method I saw on another thread about localnetgroup or something like that.
I tried to put steam as the exception for the DEP
I turned off firewall, and my antivirus system (Which at the time was Norton) but now I use AVG, and the problem remains.
I updated my Nvidia driver so it's up to date.
I tried changing screen resolution. I tried re-installing it. I TRIED EVERYTHING. YET I STILL CAN'T RUN MY 2 FAVORITE GAMES: TF2 AND PORTAL R%&*^*473UIhjg#j

I don't know what to do anymore :[ Halp me guys.

Here is what happens:
When I open steam, I double-click Portal. But it doesn't open. The sign "HL2.exe stopped working" appears. Then vista automatically search for a solution. Then it says "Solution not found, window will not close this application" or something like that.

I can't run Half-Life: Deathmatch either.
However, the strange thing is that when I open Half Life: Lost Coast, it works perfectly. <_< Is my computer on steroids or something :\

Right click your Steam icon in the tray.Go to games right click the game / mod you want and right click on it.Go to properties / Set launch options and slap this in there :

-console -novid

You can also try this program that tweaks source mods Half-Life 2: Source Sauce Utility (v2.0), Half-Life 2 Downloads, Half-Life 2 Miscellaneous

Hope that works for you when I 1st started playing TF2 I went crazy......