PC locks up when playing games....

need some help here guys....

recenty, when ive been playing games my pc locks up totally (unresponsive til i reset it manualy) and some pixels on the screen go different colours (normaly pink, blue and green)... here is the list of games i play on a regular basis:

Unaffected games:
TF2
Crysis
Farcry 2
STALKER: Clear Sky
Left 4 Dead
Age of Conan

Affected Games:
Counter Strike Source
Half Life 2 and the episodes
Guild Wars

The PC im running on atm has 2Gb RAM, Nvidia 9800GT, Intel 8400 @ stock (3.00GHz), Windows Vista Ultimate 32bit edition. I have tried updating the drivers for my GPU...

thts wot i thought before, i used a program called everest to check to see if any of my components were overheating but my gpu was running at about 50c which im guessing is a good temp. im also using this case (not the best case but i think it shouldnt suffer from overheating)

http://www.falconcomputers.co.uk/p [...] ts_id=2795

i only tried everest once so u will try your suggestion just to make sure

This is what I dislike about the auto controlled fan speeds they don't seem to be working correctly especially on Nvidia cards. I use Riva tuner, (or you could use the nvidia tweaker thing) to manually set fan speed. When I had an 8800gt, the thing never, left 20% fan speed no matter how much stress it was under unless i manually set it. My current MSI 9800GTX+ is "better" at the auto control, but still. at 60 percent fan speed the thing never breaks 60c.

So to the OP, try getting riva tuner or using the nvidia control panel to manually set your fan speed on your card. ATI tool is an excellent choice (as an above poster mentioned) to see how hot your card gets. Without having to run a game and alt-tab out of it to check your temps.

Although its odd to me some games you run fine, especially crysis.