Mobo/GPU or chipsets or ... ?

Some time ago, I posted the following on this forum:
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<A HREF="http://forumz.tomshardware.com/hardware/modules.php?name=Forums&file=viewtopic&p=551168#551168" target="_new">http://forumz.tomshardware.com/hardware/modules.php?name=Forums&file=viewtopic&p=551168#551168</A>
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Well a while ago I started having problems with my computer. The computer started freezing during some applications/games. I thought the problem was the video card or driver, but reinstalling Windows XP/2000 didn't do the trick. However that the video card was still working on other systems with different mainboards, it began to free more and more on my mainboard (Epox KTA7+). When it started freezing @ bios, I changed my Gforce card to and older ATI card. This ATI card didn't have any problem. I really don't know where the problem lies. The mainbord works with another video card and the the video card works with another mainboard. I checked the temperature of both devices (the CPU and the GPU), both were stable, even near craches. I'm afraid of buying something new, for I'm not sure where the problem lies. Is There anybody that experienced the same problem and got to the bottem of it ?

Thx
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I had some responses telling me to change my PSU to 350 Watt, for it was only 250 at the time. I did this and still have the same problem. Only now It crashes even faster and even my old ati card doesn't work anymore. I have NO clue at all what could be the problem. I can't go change all my components to see wich one is causing this.

Thx

Michiel Nuytemans