My pc freezes at gameplay (etc)

[TomasMo]

Hi all.

I have this ANOYING huge PC problem. Whenever i try to play any 3d-game or if i am watching some videos on youtube for longer then 45 minutes in a row my pc just freezes. This started happening when i bought a totaly new computer (Costume made (by me)) (That means that i have got RAM on my own, Graphic card on my own, motherboard on my own, hardriver on my own etc etc. )
So now, when i try to play any game (Stronghold:Crusader, mount&blade, C&C Generals, GTA san andreas, Call of duty 2 and 4, Halo etc. etc.) my pc works just fine, for 2 minutes. It hase no problems during the menu, or when i create my character in mount&blade, but when any of those games start, its hell. They work fine for max 2 min (Halo works around 35 minutes) and then my PC, mouse, and everything else freezes. After 1 minute of everything being frozed, the screen turns black, like the computer is not even on. But the good news is that i can still play smaller games (fallout 1, fallout 2, Fallout brotherhood of steel, outpost 2: divided destiny, age of empires 2 etc.).

Details about my computer:
AMD Anthlon(tm) 64 processor
3000+
1.80 GHz, 512 MB of RAM

Microsoft Windows XP
Home Edition
Version 2002
Service Pack 2.

Thinks that i have tried:

Runned a mem test - all fine
Formated and reinstalled my windows - all fine
Checked for over heating issues - all fine
God knows what i haven't tried - all fine
Bought an additional cooler

Ohh, and by the way, when i turn off my graph card i can play Stronghold Crusader, but it only works on that game.

SO IF YOU ARE ALL SO GOOD, HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!!!
I am gonna be viewing this topic 24/7, so please give me any tips or hints on what to do!
Just tell me if you need to know anything else.

[TomasMo]

Ohh, and when i disable my graph card my pc dose not freeze. Maybe that is somewhat important?

[fmc-tech]

Sounds like a heat issue to me.

[TomasMo]

Well its not, i have 2 coolers, and some weird metal bars cooling my graph card. And i use SpeedFan and all my temps are whitin acceptable limits.

[TomasMo]

Ok, i am now totaly sure that it only freezes during gameplay. And i have 3 coolers and i even puted my room ventilator to cool my pc, but i still have the same problem.

[TomasMo]

Ok, i have a new clue! Sometimes when the game freezes i got a message that "infinite loop" happend, that helps a bit?

[annihlator]

It quite definately is a heat issue.

You seem to say something about "weird metal bars"... What graphics card ís it? (the exact one).
I have a gut feeling it either is a passively cooled one, or perhaps you may have changed it's cooling, if you have removed its cooling in the past, you should apply new heatpaste because you probably either forgot that or messed it up ;)

And/or perhaps a picture of the situation of your graphics card?