Hope I am not off-topic by posting a hardware question in a software help website, but you guys have been so helpful with my linux hiccups, so I thought I'd give it a shot.

My Desktop runs Windows XP Pro. I recently 'upgraded' - new processor, new motherboard, new RAM, new case (stupid Dell and their 'almost' ATX case). Here are the system specs:

New Parts:
AMD Sempron 2500 (Socket A - 333MHz FSB)
ECS KT600-A Motherboard (jumpers set to 166 MHz system bus - i think this is OK, some sort of multiplier)
512MB Mushkin Green Line RAM DDR 400 RAM
Raidmax Mustang Case (with cool lights!)

Old parts (from the Dell Dimension 4100):
20 GB Hard Drive
Video Card
Linksys WMP54G wireless card

The computer was hanging at random times after Windows would boot. Could be many things, I'm not a total newbie to system troubleshooting. So I ran memtest86. The system froze during the memtest. I ran it again and was lucky enough to complete the test this time - no RAM errors after 2 runs.

The case comes with a neat LCD temp display - I hooked the sensor onto the processor heatsink, not wanting to mess with shoving it underneath, even though I know its not the most accurate reading. All the fans are running and the screen says the temp is 30-32 Celcius (even during our 'heat snap' yesterday the temp didn't go above 39).

I am assuming that I either have a Motherboard problem or a Processor problem, since it froze during a memtest, and the subsequent memtest told me the RAM was good.
Is this a valid assumption?
(Can I rule out a powersupply problem? The Mustang PSU is supposed to be pretty good, its rated at 420W, far above my meager needs, and everything stays powered on during the freezes)

Low-end ECS boards appear to have a smattering of quality control problems (based on anecdotal evidence I've browsed on the web), but I don't want to return the wrong part.
How can I determine whether the processor or the motherboard is the problem?

I am familiar with using my Knoppix CD to troubleshoot hardware (have used for Hard Drive problems on other systems in the past) can this be used for the job?

Have you cleared the bios and gone to default? Actually, I would put the problem on either memory or an add in card. The processor is going to low likelihood, the motherboard, oddly enough will also be unlikely, but possible. You need more testing. Bring it up barebones(video, 1 floppy, keyboard, mouse, 1 ram dimm) and test it with a dos based testing program, stress test it. Add in cards slowly, stress test again. I am assuming you used a clean install of windows, as it doesn't migrate well at all.

Thanks for the reply.
I did reinstall Windows.
Can you recommend a good DOS based testing program?

After some sleuthing, my preliminary assessment is that one of the PCI slots is causing problems. With the wireless card (the only PCI device) in the slot closest the processor, the hangs happen. With it removed and/or placed in the farthest PCI slot everything is AOK - at least so far, the hangs are unpredicatble enough that some have occurred after a few hours of uptime.

During the testing, I noticed another symptom - windows takes over twice as long to boot with the card in the suspected 'bad slot'. Plus I was able to create crashes during memtest with no IDE devices on - some even occured while the BIOS was scanning the IDE bus just after boot.

If I can get good uptime with the bottom slot, I will put the card in the bad slot to try and reproduce the error (make sure it was seated properly before).

Which leads me to my question. Is this symptomatic of a bad PCI slot, and the Mobo must go back, or is there some sort of possible software problem I can fix without the return?

Well, the pci slot nearest the processor on some boards is the slot that operates at 66mhz(mine has 3 such slots), while slots further down operate at the standard 33mhz. I have a fibre channel card that won't operate at the 66 mhz, though it is supposed to, but will operate at one of the other slots. Symptoms when I put the card in are anywhere from not even booting, to having to power off after windows shuts down or it won't come back up, to occasional blue screens. Try another card in the slot. If it works, then it might be the card isn't set to work only at one speed, and defaults to pci speed whatever it is.

Then again, it could be the bloody slot...it happens.