Halflife 2 Bug Issue

[chicken]

Whenever I play Halflife 2, or even Portal or Slender, after awhile the graphics begin to get flashy and sometime the polygons have a long pointy object that protrudes out of them, (it's hard to explain) then eventually my computer freezes and I'll have to shut it off, and when I turn it back on there are sometimes quite a few discolored pixels on the start up menu. They eventually go away. And if I'm lucky, the game will just crash and on my desktop there will be multiple discolored pixels. Does anybody know what the deal is? I've lowered the graphics on my HL2 but it's still freezing. I've never had this problem before until now. My graphics card is up to date and I have Windows 7. Thanks!

[Vincent]

I've seen something similar, but i don't know how to fix it...

[chicken]

Anybody know of a method of how to fix this?