Intermittent "Won't Boot/Post" Issue Turns Permanent

[DKlein]

So, over the past maybe 6 months, my computer started to stop starting on random, rare occasions. Maybe once every month or two, suddenly the power switch did nothing. I would fiddle with the PSU cable, thinking that was the case, and after a few minutes of fiddling, the thing would turn on and be fine for the next month or two. I suppose this is not evidence of a direct causal relationship, but it sure was correlated well.

Then, fiddling didn't work.

A new cord didn't work.

A different PSU didn't work.

Do what now?

So, after taking it in to the local computer shop, we found out one additional piece of info:
- It only turns on if the 8-pin is disconnected.

Seems like a dead motherboard then, but then how does a motherboard die and get revived so many times by jiggling the power cord?

Any ideas on the issue? Other than this, the system wasn't experiencing any problems, stability issues, random reboots, etc. I'm in Vietnam, so maybe the local power supply was the culprit... ?

ASRock m3a770de
AMD x4 925
2x2GB OCZ Z-series
OCZ Z-series 500W (about 150W more than needed with 25% efficiency reduction even)
GTS 250
(Never OC'd)

Needed an overhaul anyway, but I'm just curious. System was just shy of 3 year birthday.

 

[lakedude]

I've got a Dell that has gone through the same progression. After fiddling with memory, cpu, video card, hard drive and PS connections the computer would run fine for months but eventually it would bomb out again.

This last time it did not come back on even after much fiddling...

I suspect my MB, will get back to you if I ever get around to replacing the MB.

The stupid OS goes with MB so I'm dreading the call to M$ explaining the new MB situation.

 

[denis280]

if you disconnect the power button from the mobo.and use a flat screwdriver. jump the two pins.for on and then for off.

 

[DKlein]

Well, considering I can power the computer on when the 8-pin is disconnected, probably the power button isn't at issue

2 shops: both tell me that, from their experience, it's the mobo and irreparable, though no definitive cause has been given. Physical inspection of the mobo reveals no apparent damage save minor rust at some MOSFET sites and some slight scarring from an errant screwdriver (the latter of which is unlikely to be the culprit). Perhaps the humidity got to it (in the tropics)... but I don't know how much rust is too much (it's very little).

Even if I replace this (wanted an 1155 anyway - AM3 is a bit old now), I still want to locate the fault. It's basically impossible to test the CPU as the culprit without doing it myself since the shops here A) aren't really doing much to check (i.e. not actually using tools to test for faults) and B) don't carry AMDs to swap it with.

 

[DKlein]

First, I've tested both sticks of RAM individually. Both seem fine.

I took the GPU, CPU, and PSU to a local shop that has AMD products to do a check. Gave the guy the CPU, we fired it up past POST and BIOS screen. Guy had no background knowledge of my issues (language barrier and all), and just told me "likely mainboard." Insightful, eh?

Hooked up the GPU anyway, worked just as well. "Likely mainboard" again.

Asked him to test the voltage on the PSU, but it got lost in translation. At any rate, it's working.

So, I'm going with "likely mainboard". Won't get a definitive answer ever, but I'd put money on some part of the voltage circuit having died.

I'll be sure to keep a close eye on my voltages with the new build - still suspecting the PSU.