Custom Built Computer Won't Turn Back on Sometimes After Power Loss or Shutdown

hello experts,

we have a client with a custom built computer that she has had for about 5 years now.  It has worked great without any problems but lately after a power outage or sometimes (this is what the customer reports i haven't been able to verify this) after a windows shutdown the computer will not power back up properly when turned on.  the fans spin up and led lights turn on but there appears to be no post, there is no video or beep either.  so to fix the issue you have to unplug the power from the PSU (corsair 750 watt) press the power button to drain any residual power, and i'll also turn off the power switch on the PSU, press the power button again for good measure, and then plug it back in, with the power switch off.  then i'll flip it back on, press the power button on the case, and it works just fine.  I'm thinking that its either the motherboard or the PSU but I want to be absolutely sure before i recommend any replacement hardware.  this computer is used by an elderly woman and carries a very large sentimental value to her as it was built by a family member that died recently, so i want to replace as little hardware as possible.  Any suggestions are welcome, I know i had this issue before with a cheap PSU and i replaced it with a corsair PSU exactly the same as the one she has now and i've never had any issues, its been running strong since early 2010, so i wouldn't think it would be the psu, but even corsair isn't perfect, and her computer is on almost 24/7, far more than my gaming rig that my psu went into.

Thank you  in advance for any help.
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Check motherboard for blown or bulging capacitors which could cause this behavior.  Good news is, inexpensive to replace.

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ctagleAuthor Commented:
We have a site visit planned for tomorrow morning, we'll check that out and I'll report back here tomorrow.
I'd also look at cracking, bulging or leaking electrolytic capacitors first (Also within the PSU). Although they are cheap, you need some soldering experience to replace them, so it is not something everyone will be prepared to do, and it may take more time and therefore cost more in the end than just replacing the board or PSU.

Besides that, replace the CMOS battery and clean out all the dust. Remove the heatsink from the CPU, clean both surfaces very thoroughly, apply a very small drop of fresh thermal transfer paste to the top of the CPU, and firmly and properly reattach the heatsink.
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i also suspect the bios battery  -repplace it, irt is a CRC2032 and should read 3 V min if you want to check it - aand it costs about 1$
so that would be my first step

"I know i had this issue before with a cheap PSU and i replaced it with a corsair PSU exactly the same as the one she has now and i've never had any issues"

I may be misinterpreting/misreading what your saying here. but if you've had the same problem before, then surely you already know what the issue is?  With regards to Corsair, I think they're supposed to be really good, but everything will fail at some point.

It certainly however does sound like it could be capacitor related.  This might sound rather obvious (or maybe not), but if you're going to delve into the PSU itself, just make sure it's disconnected from the mains before you do.

Out of interest, you use the word 'client'.  Do you fix PCs as your job?
ctagleAuthor Commented:
Issue appears to be resolved.  Got them to buy a better UPS and configured auto-shutdown and initial testing shows that the issue no longer exists.  I would guess its some kind of safety in the PSU when it loses power abruptly, but I could be wrong.

In response to your comment IT-Expert:  I was looking for a second opinion and was trying to provide as much information as possible, that's the purpose of the post, I wouldn't have made one if I knew for sure what the issue was.  Corsair is very good but that goes back to the original point of second opinion.  Overall the only partially helpful part of your post is when you parroted what other users mentioned about the capacitors, the rest of it appears to just be condescending, and as this is a professional forum, I will not address your statements or that last question other than if you aren't going to be helpful or suggest a new idea that the others have not, then don't post on the question.  To the rest of you, thank you very much and have a great day!

I don't know if you will be reading this or not, but:

I realise that you were looking for a second opinion/advice from others.  Without going into great detail, I responded to your original post in the way that I did (highlighting part of what you yourself put), because at the time, I found part of your post puzzling.  I may of 'parroted' what other users mentioned, but I also gave you advice on potentially fixing the possibly faulty PSU.  You are absolutely right that this is a professional forum, and any response I give is generally either providing potential solutions to a problem, or asking further q's to get a better picture (possibly because I personally may feel that I need further information or maybe I don't understand part of what an OP puts).
With regards to being condescending, that was certainly not the intention, however......

At least you've found a workaround to the problem.
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