Stone dead and all out of ideas

[domesis]

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Okay, so before anyone asks... I HAVE read the sticky at the top of the forum and tried everything possible to no avail.

The story so far: Several days ago I was using my PC as I do without any problems at all, it had been running smoothly as it always does (P4 3GHz, 512DDR, XP PRO, ASUS MoBo - unaware of model, 120G HD). I had just that day acquired a brand new MP3 player which had just then finished charging. It required no installation of drivers so I attached it to its AC adaptor and connected it via USB according to its manual. The instant of connecting my computer immediately lost all power, and has since not been able to start up at all. No fans moving, no HD activity, no beeps and no lights. The MP3 player I have since attempted to use in 2 other computers which it didn't ruin, so I am still unsure whether it was the cause.
The only sign of life in the PC is the motherboard light is on when the power button at the rear is on. Other than that it is stone dead.

Since then I have reset CMOS by removing the CMOS battery for several minutes. I have stripped the PC back to barebones with nothing but the GeForce FX5200 graphics card, 1 512 stick of RAM and MoBo + Processor. Same results.

I have used the power supply in another computer without problems, so it isn't that. I have also used the HD as a slave in another computer which obviously also wasn't the problem (as discovered by bare bones). I have also attempted to power on by using a screwdriver to short the power pins. No dice.

I have ensured that every cable is correctly connected, every card etc is seated properly and every neccessary switch turned on. I am at a loss as to what I can try next. I'm thinking at this point that it looks like either a CPU or MoBo problem which I'll haveto go out and replace, but would like some clarification before I do.

Any help would be greatly appreciated. Thanks.

~Domesis

[Sylvander]

Once upon a time...

I connected a USB plug into a USB socket THE WRONG WAY ROUND.

As soon as I did so, there was an ominous CLICK, and the PC powered off.
So long as that was still connected the PC appeared DEAD.

When I plugged it in the right way round, everything came back to normal.

Does my little story give you any ideas?

[Paul Komski]

it looks like either a CPU or MoBo problem
Agree - that's what it looks like alright.

[deddard]

Welcome aboard!

Looks like you've covered most of the bases. A MOBO or CPU is the most likely, and the only way to test is to place the cpu in another mobo.
It's possible that connecting the USB created a short - is there any smell of burning on any of the components (the southbridge is the place to start) or any discolouration?
The biggest problem here is that these things can just fry without giving symptoms. Bulging capacitors etc can also be a sign of things frying, but you need to figure out a cost/benefit ratio of continued troubleshooting vs getting a new mobo/cpu. You're the only one who ca decide this, as testing dead mobos is nigh on impossible. If the CPU works ok in another mobo, you're ok, but the mobo isn't really worth huge amounts of time troubleshooting - you'll end up pulling your hair out.

One thing to check is to see if the USB connectors are connected by jumper pins to the mobo (some are) if so you could remove them and see if that cures the problem.

[DigitalJ]

One thing to check is to see if the USB connectors are connected by jumper pins to the mobo (some are) if so you could remove them and see if that cures the problem.

This would have been my first guess. Have you used that particular USB slot before without a problem? Especially if it's a front end slot, some case manufacturers seem to think they should make it as difficult as possible to hook up a USB slot by separating all of the wires. It's real easy to mix one or two of them up since the mobo never has the same markings.

Unless the USB slot is onboard, I would unhook all of the wires and try powering back up to see what happens.

Bummer, though, dude.

[domesis]

Once upon a time...

I connected a USB plug into a USB socket THE WRONG WAY ROUND.

As soon as I did so, there was an ominous CLICK, and the PC powered off.
So long as that was still connected the PC appeared DEAD.

When I plugged it in the right way round, everything came back to normal.

Does my little story give you any ideas?

Yeah, unplugged it as soon as it happened. I had originally hoped it would be so simple.

One thing to check is to see if the USB connectors are connected by jumper pins to the mobo (some are) if so you could remove them and see if that cures the problem.

Yep, it is connected by pins to the motherboard. I tried that a few days ago and unattached the front USB ports. Still didn't work. Exactly the same response as every other attempt - ie nothing at all. No burning smells or noticable burnt areas etc that I can see either. I have used the front USB ports before... but who keeps track if I'm using the top or the bottom one usually? There's a good chance the one of the two I did use hadn't been used before now.

I don't have access to another MoBo capable of handling the CPU to test so it looks like buying a new MoBo and hoping that fixes the problem. Thanks for your responses guys. Now it's a matter of finding time to go purchase one. Until then its using an old flat mates 433MHz celeron.... *shudders*. God help me.

~Domesis

[jlreich]

You might consider taking the mobo and the CPU down to your local computer shop and have them test them both. It might cost $10 or $20, but you would know which one is bad. That's better than buying a new CPU and then it turns out to be the mobo, or vice versa. ;)

[deddard]

Last ditch for me would be to unplug the keyboard and mouse and try to power on - my reasoning is that if the southbridge had a problem, it could have taken out the keyboard, which in turn could prevent anything from starting next time round. It is a complete shot in the dark, but simple enough to try.

[domesis]

You might consider taking the mobo and the CPU down to your local computer shop and have them test them both. It might cost $10 or $20, but you would know which one is bad. That's better than buying a new CPU and then it turns out to be the mobo, or vice versa. ;)

Only problem with that is I have no car, and I don't really relish the idea of lugging my motherboard/case or whatever around on public transport. So I'll go for the easier (and possibly more expensive) route. I'll make sure I give them a run down of the situation before I buy anything to possibly help any returning I may wanna do if it doesn't fix it.

~Domesis

[domesis]

Last ditch for me would be to unplug the keyboard and mouse and try to power on - my reasoning is that if the southbridge had a problem, it could have taken out the keyboard, which in turn could prevent anything from starting next time round. It is a complete shot in the dark, but simple enough to try.

Yeah, tried that already too. I'm just going to bite the bullet and go get the MoBo and hope all is fixed tomorrow. I'll post the results here.... hopefully with good news. Thanks everyone.

~Domesis

[domesis]

SUCCESS!!
Okay, so I went and got the new motherboard. Everything is again running perfection... Plus the new motherboard is superior and I got some more memory while I was at it. So now the computer is better than it was (lets ignore the fact money was spent). Thanks everyone for their help! I don't know which part of the old motherboard was dead.... but at this point I really don't care. :p

~Domesis