Strange Graphics Glitch

One day a few months back i started Gmod up just after updating it, though i have played over 300 hours of Garrys Mod i have not yet encountered this glitch before, it happens every time i play and does not fix itself.

Here is a picture of what i am talking about

i also observed this happening with Counter strike source and Team Fortress 2 also, but not with HL2 mods like battle grounds or insurgency

If you can, your help would be well appreciated.

GPU overheating

Happends on my 8800GT. I believe it’s an overheating GPU or dust.

Either an OUTDATED GRAPHICS DRIVER or your GPU is overheating.

ALWAYS try updating the drivers first.