PSU Clicking Problem, Funny Test Result; HELP!

Hi guys, I'm not able to get a client's pc to boot up.  She says one day it just stopped booting up, out of nowhere.

I'll break this down so it is easy to see where I'm at:

1. problem:
no boot up at all

2. symptoms
clicking PSU, blinking LED light on PSU

3. what I have ALREADY done:
removed motherboard from case,
disconnected everything (except USB ports and keyboard/mouse ports),
laid MOBO on a wooden table (to rule out shorts).
removed the 20 pin connector off the MOBO and "jumped" it, using a scrap piece of wire- going from the green to a black wire.  When I do this, I get a normal PSU behavior, fan starts, and it tests out at specifications except I get a 900ms time, rather than the specification-mandated 400ms
*could this be triggering a problem elsewhere?*

Hence, I have a PSU that is getting power, putting out normal power ranges all the way to the 20-pin, with no clicking or "tripping" while I use the old wire jump trick on the 20-pin.  As soon as I put it into the motherboard with really very little or no load, I instantly get the clicking again, and no dice.  The only anomaly I can find is the 900ms on the PSU.

The only thing still connected to the MOBO is the all the little USB ports, the keyboard/mouse connectors, and the dial up cable port.

I am trying to trouble shoot and I guess my question is should I try a new processor, or go ahead and stop being lazy and take off all the USB ports, mouse/keyboard ports, ethernet port, and other stuff until I ONLY have the CPU on the MOBO?

My hope is that by presenting everything I have already done, that it might be already apparent to someone else looking at this problem, and you can tell me what is dead or what is the culprit, especially if you've already dealt with this before, or in the case where it is obvious to you already what the problem is.  It seems like working on PC's is like working on complex math problems: it is always good to have someone else check for errors in your work, since they are less likely to keep repeating the same errors you have.

Thanks in advance for the help!

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edbedbConnect With a Mentor Commented:
If it were to happen to me, the first thing I would try is another PSU.
Tony_the_PC-TunerAuthor Commented:
Thanks, edbedb.

I have tried another motherboard, and here's where I am at:

I can connect any working PSU, and I can get it to power up by "jumping" it with a scrap wire.  This is WHILE THE PSU is connected to the MOBO with the 4-pin power cord.

But, if- instead of using the "jump" wire, I plug in the 20-pin to the MOBO, I try to use the power switch to fire it up, I get nothing but clicking and flashing LED, telling me something is tripping it.

What's the best way to determine what is tripping it?  I don't have another CPU laying around that I can throw onto the board, and all the rest of the stuff (USB ports / keyboard port/ethernet port) is hard soldered onto the board, and therefore not removeable.

What am I missing here?  Do you know of any kind of list that exists for trouble shooting this?

At this point it seems like the problem of shorting out must be either in the MOBO or the PSU.  But I'm stumped on this, and I have the feeling that the answer is right in front of me but I just can't figure it out.
Tony_the_PC-TunerAuthor Commented:

I meant to say I have tried another PSU (in sentence no. 2)
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Any bulging or leaking capacitors on motherboard?
edbedbConnect With a Mentor Commented:
If it's doing the same thing with another PSU I would have to say that it's your MB.

If you want to see if it's the CPU just pop it out and try it. Noe a definite test but it could tell you something.
Tony_the_PC-TunerAuthor Commented:
So you're saying pop out the CPU, and then try to get it the PSU to power up with the power button- but without the CPU installed?  I will try it!
Tony_the_PC-TunerAuthor Commented:

No bulging or leaking on the MOBO that is readily detectable, after a very close inspection.
willcompConnect With a Mentor Commented:
Could be a faulty cap without external signs, a faulty MOSFET, or another one of the myriad components on a mobo. Is there a reason you can't replace the mobo?
Tony_the_PC-TunerAuthor Commented:
The problem persists, sans CPU.

@willcomp:  There's no reason I cannot replace the motherboard- which it looks like is the culprit as near as I can tell.  This is about as fine a resolution as I feel I'm going to be able to get.  The whole thing was more about troubleshooting to the point where I was able to positively lock down that the problem was the motherboard rather than the CPU.

I think this wraps up what I'm able to do at this point, but based on what you've read, would you concur that something is up with the MOBO?

The PSU only clicks when the 20-pin is plugged into it, and it has essentially been stripped of everything including the CPU now, and is not touching anything conductive.  Any final steps to recommend, or am I at the end of the road when it comes to testing other components?

willcompConnect With a Mentor Commented:
I don't know anything else to try. Symptoms are not those of a short which leads me to think you have a faulty component in the mobo power circuitry.
As long as I understand you correctly that you tested with a know good PSU a bad MB would be my guess.
Tony_the_PC-TunerAuthor Commented:
I'm going with this as the final diagnosis.  I don't do too much hardware stuff, so this is a huge help.

The replies are very much appreciated, and that's the direction I'm going in.  For what it is worth, I'll post here in a day or two with follow up results, after a new MOBO arrives.  

Thank you again.

nobusConnect With a Mentor Commented:
you can still do some testing, if you have a volt meter around  - on the 24 pin plug, check PSon, and PWRgood voltages :
see the readings under the connector
Tony_the_PC-TunerAuthor Commented:
Well, here's the deal: Turns out it I had a bad PSU and also a faulty motherboard.

When I got the new motherboard, I connected it to the old PSU, and it started to POST and then died.  Then I had the same clicking/tripping issue.  

I pulled it out and put a new PSU in, and presto!  Instant startup, and no issues at all, after that.

Thank you so much for all the help, folks, I certainly appreciate it.  

I passed the point out as best I could since everyone's input helped me arrive at my solution.  Thanks again.
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