Computer crashing... need help

[Teddy]

My nephew brought his computer over for a lan. This was last friday when the tempature out side was like 5 degrees outside. once it was plugged in, he turned it on and it started to power up and slowly powerd down.... At this time he caught my attention that he had tried to turn it on instead of letting it warm up and dry out(condensation was building up in the case since it was just brought into our nice warm and humid apartment). He waited 30 min and it powered up just fine....until 3 days later. The first problem was we noticed a few crashes and that the system seemed to be running slow... our first reaction was it was a virus(since he just brought it over from lanning with his friends). So a norton ghost and virus scan later,we found that didnt fix the problem!!!!
I then looked at hardrive and sure enought it was running in PIO mode instead of ultra-dma... and as long as the hardrive is hooked to the primary/master channel it runs only in PIO mode, all the other channels it runs in Ultra dma.... so i figured at least the primary channel is toast:(

Other than that... the memory tests fine when using a memory tester that boots off of a floppy but have no way to really test the cpu or motherboard(or whats left of it). The system is completely unstable now and crashes almost instantly once booting all the way up. Any recomendations as to what i can do to narrow down what is wrong here? the only hardware i can't test is the power supply, mobo, and cpu. The athlon 2000 and cheap via board are ready for an upgrade anyway, so that i will gladly replace... but i really would like to find a good way to test the psu....

[Mr. Perfect]

I don't think it was because of condensation, but during one summer after moving a PC I had the mobo go slowly insane. First it started loosing things on boot(would "miss" a drive or something), then it got to restarting itself after random periods, and finally wouldn't boot at all. Sounds like your PC is doing similar things, so perhapse it's the mobo.

[Vindicator]

You can check the power supply voltages with a multimeter (how-to here), or just grab a tester. I'd check that, then the mobo.

I killed a laptop system board by using it in cold weather and then taking it inside, so its possible that something broke when your nephew did that.