Source games... HELP

[Kala]

So... I bought Counter Strike: Source and Garry's Mod from steam. Does anyone know these games? They doesnt work on my computer... It just gives me a error. When i launch the game, it loads few seconds and then i can see the main menu. But then, it crashes, saying : hl2.exe has stopped working.

Specs:

Intel Celeron CPU 900
2.20 GHz
3 GB RAM
Windows Vista SP 2

My computer should be able to run these games easily, so wheres the problem? I have tried to update all my drivers, reinstall games, tried all -dxlevel codes etc... Can anyone help me with this? I would appreciate any answers... Thanks!

 

[Kercyn]

Oh look!
1st result

 

[The Reborn Devil]

I got those errors myself when I got Garry's Mod too, but I have Windows XP SP3.
Once I reformatted my computer it worked like a charm. Dunno if it was required though, but my computer was slow and needed it anyway. Could also have something to do with your hardware or maybe some corrupt files. You haven't posted your GPU, but your CPU isn't exactly good. If you have added any addons they might cause some problems. I remember I got some errors after I added some tools for Wire mod.