Lighting issues with gmod and other source games.

[Gramps]

Hello There facepunch community!

I am in need of assistance, just as the title says there are lighting issues with all of my source games. Gmod,Half life, counter strike,L4D2, some half life mods ect.ect. tf2 runs fine for some odd reason which im happy about. I have already contacted Steam support for this issue and they kept on bringing me back to square one. So now i come to you for help!

I have re-installed the source games numerous times, verified the game cache and wiped all addons from gmod. still nothing fixes it.

Here are my pc specs.

Processor: Intel Core i5-3350P CPU @ 3.10GHz
Ram: 6 GB
Graphics card: NVIDEA GeForce 7900 GS
OS: Windows 7 Ultimate 64 Bit.

Now i am thinking it is the graphics card, but i don't see a reason why it should be.
I have been dying to make decent gmod pictures and have games run properly.

Please let me know if there is anything else i can provide!

Thanks in Advance, Gramps