Weirdest computer problem...EVER
 

Ok, I really hope you guys can help me out, because this is way beyond me.
Today I assembled a computer for my girlfriend, something I've done lots of times before. So, all is well, I start the computer, enter windows and installs everything for her. When I'm finished, I close the case and stand it up. After a few minutes, the computer shuts down, just dies.
I'm wondering WTF and opens it up again, all looks to be alright. I turn it on, only to have it die on me almost right away.
After some time swearing and messing around, I figure out that the computer works just fine, as long as it's lying on it's side! When I stand it up, it's just a matter of time before it dies without warning.
Now, I suppose I could let my girlfriend use the computer lying on it's side, but somehow I doubt she'd like that.
Anyone has any idea what could be causing this? I have no ideas left...

You most likely have cooling issues. When most processors get to a certain temp, they shut down to prevent them from melting. What are your specs? It's also possible that your power supply might be bad too. What type of case is it a tower or one of the old horizontal cases?

It's a AthlonXP 2500+, 512 MB PC3200, Silent Viking II CPU fan. I would agree with you that it could be heat issues or a bad PSU if it weren't for the fact that it works flawlessly when it's lying on it's side. If it were heat or a bad PSU it wouldn't work even if it were lying down, right?
Oh right, it's a midi tower case with lots of space left, so it's not very hot.

Is something loose on the inside? Maybe the cable for the PSU or the mobo isn't fully seated, and makes a better connection on its side.

Had that happen to me as well, checking out a customers build, I found that the motherboard mount was not quite right. With a little investigation, there was a loose screw shorting out the motherboard. Another thing to check for I guess.

What's the temperature of the CPU and motherboard in the BIOS setup?

Yeah I've been thinking about if it could be some kind of short. I was took the mobo out and fastened it again, but still this issue. I will look a little closer since I didn't see anything.
The CPU temp is well below 50C (Whatever that is in Fahrenheit) and the motherboard just over 30, so heat should not be an issue.

I'm jumping on the "you have a short" bandwagon. something is probably lose and/or touches when the computer is standing up.

Or something is not grounding properly. No blown capacitors on the motherboard?

Well not that I have noticed no, and if it were would it work lying down?
Bad grounding keeps floating around in my head, read somewhere that if you don't use enough little studs the mobo (Abit NF7-S) wont be properly grounded, causing this problem. Sounds sane to you guys or is that just BS?

Unplug everything.
On MB, install CPU, Memory (1 stick only), Graphics card.
Add power to the MB.
Plug in mouse and keyboard and Monitor.
Turn it on and check the bios, particularly the bios health indicator. Usually has temp in there.
Watch it for a bit.

If ok, add HD, same process.
Add CD/DVD. Keep monitoring.

Keep going until you find what breaks it or until it's stable.

Do a close inspection on the MB, look for hairline cracks. Make sure the little stand-offs

Do a close inspection on the MB, look for hairline cracks. Make sure the little stand-offs are fastened securely before you put the MB back in. Put back minimal components as suggested by WillyPete. If you can get into Windows now, perfect, let it run screensaver or something continuously for a day or so. If you can get a copy of Sisoft Sandra Pro, run the burn in test. Good luck.

The number of standoffs sometimes matters, it'll be in the manual or update on the website. Sometimes the motherboard manufacturers cheap out by running a ground through those standoffs. So it's not insane at all. But the previous posters methods of doing a 'minimum to maximum' installation of parts will help identify the bad parts, if those parts are bad.

As well with the SANDRA burnin test program, there are specific ram check programs. I vaguely remember one ISO from a linux site that did nothing but check ram and do tests on it. May want to take a look around for that. If I find that site, I'll post it up.

Many chips will trigger auto shut-down if they get too hot. You can either get hold of a temperature sensor, or you processor may report its temperature to the screen.

Here are some links to check out:
http://www.maxim-ic.com/appnotes.cfm...te_number/3173
http://www.hmonitor.com/

Here's a freeware monitor: http://www.almico.com/sfscreenshots.php

I had a similar situation once and it turned out to be a loose Northbridge heatsink. Somehow the mount for the heatsink had broken and it would not make good contact while it was standing up. I couldn't figure out how to fix the mount and I was too cheap to buy a new heatsink, so I just coated it with some Arctic Silver and viola... it worked.

It’s even better to take the motherboard out and place it on the static bag, and tests it there, it sounds like it’s a short, as a component heats up it expands and shorts. Other then that, the heat sink could be losing contact when it is standing up, look at that too.

Well, I removed the CPU and heatsink and reseated both, adding some more thermal grease and so far it works. No unexpected shutdowns. Thanks for your help guys

I wonder if it was the actual insertion of the CPU and sink?

You said after you took it and added some thermal grease it works fine, maybe it was not in all the way and once the heatsink and fan started running it was enough to wiggle the cpu out of place and laying it back down on its side was just enough pressure to make contact for it to work.

That or the grounding issue would have been my two guesses.

Yeah I'm thinking the CPU wasn't inserted properly. When lying on its side the CPU cooler would then press down on it making it sit tight in the socket, but standing the case up would relieve some pressure from it. Anyway, it works just fine now, hoping for the best...

Keep an eye on the machine, you should run a burn in on it. I do like the SANDRA burn in program, it'll put it through the paces.

Yup, ran SANDRA burn and it passed without any problems.