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Inexplicable problem - help greatly appreciated

Last response: in Systems
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September 12, 2011 7:10:38 PM

I built my current system two years ago (with some help from this forum, thanks guys/gals) and it's been working fine until a few weeks ago. I left the computer on overnight and in the morning the computer was off and would not turn back on. I've done a bunch of troubleshooting already, and I think it might be the processor, but I want to be sure I've tested everything before going out and buying a new (probably unreturnable) CPU. Here's where I am:

The setup:

CPU: AMD Phenom II X3 720
Mobo: ASUS M4A78T-E
RAM: OCZ Platinum 2x2GB DDR3 1600
PSU: Nexus Value 430


The symptons:

- There's a green LED on the motherboard that is on when there's a power supply connected. That LED is on.
- When I press the power button on the case, the fans spin up for a second but immediately stop. The power LED on the front of the case turns on but then fades off.
- I don't have a case speaker, so I don't know anything about the POST status.

Some steps I've gone through:

- It's not the PSU. I tried my PSU in a friend's computer and it works. I tried his working PSU in mine and it won't turn on.
- I don't think its the motherboard. My motherboard was under warranty so I sent it to ASUS for repair. They sent it back to me without any explanation. At the time, I thought they couldn't figure out what's wrong with it so I called them back and complained. They offered to replace the motherboard with the same model. The replacement came in today and I hooked it up, but nothing has changed. The box that the new motherboard came in had a paper that says they tested the motherboard before shipping it.
- I don't think it's the case switch. I tried touching the PWR pins with a screwdriver and I can hear the PSU make a noise for a second, but it doesn't start.
- I unplugged everything else (even the keyboard). I haven't tried taking all of the RAM out yet because my heatsink blocks the last RAM slot and it's a pain to get them in and out with the heat sink on. Also, without a case speaker, I don't think I'll learn much.

Final details:
- There was a big (big for Philadelphia) storm the night that my PC died. The PC was plugged into a surge protector, but I think it's possible that the storm had something to do with it dying.
- The day after it died, when I plugged my friend's known-good PSU into my motherboard, it still wouldn't turn on. After about 10 seconds of being plugged in, his PSU sparked, made a weird noise and died. It never worked again. This was on the old motherboard (before replacement).

Any ideas or other tests I should run? Thanks in advance.
a b B Homebuilt system
September 12, 2011 7:26:28 PM

What do you mean by the good psu? So your motherboard blew your friends psu too?


I'm confused.

The last thing I would suspect is the cpu. I would suspect the surge protector or power supply, possibly motherboard or ram.

I mean with a power surge it could be basically anything, but the last thing I would suspect is cpu.

Best solution

a b B Homebuilt system
September 12, 2011 7:35:12 PM
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I doubt a case speaker would even matter, since you probably aren't even getting to the post beeps.

I had the same exact symptoms years ago and it turned out to be a combination of PSU and motherboard. Not sure if the PSU caused the motherboard to fail or the other way around.

It was under warranty so I sent just the motherboard back since that is what they thought it was. I can't remember if it worked for a bit or not, but ultimately the same symptoms returned. I sent the whole PC in and they replaced the motherboard a second time and the PSU.

I wouldn't be shocked if the PSU is bad, but just good enough to start your friends computer, or it got fried after frying your friends PSU with your bad motherboard.
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September 12, 2011 7:54:00 PM

geekapproved said:
What do you mean by the good psu? So your motherboard blew your friends psu too?


My PSU (the one that is in the computer that won't turn on) is the good PSU. To test that, I took my PSU and plugged it into my friend's computer. His computer worked fine. I then took his PSU and plugged it into my computer. My computer did not start up and fried his PSU before my eyes. I then plugged his fried PSU back into his computer to verify that it was dead, and it was.

I never plugged my PSU back into my motherboard after my friend's PSU died. In fact, my friend used my PSU for several days until I bought him a new one, so I'm pretty sure it's not just good enough to turn the computer on (as nordlead suggested). I guess it's still possible that the combination of the PSU and the motherboard are what's killing it, but it seems really unlikely.
a c 136 B Homebuilt system
September 12, 2011 8:00:46 PM

big storms = lightning
lightning = power surges in the grid when lines get hit

The things that die , after we exclude your motherboard that ASUS say is working , and the psu
is RAM or vRAM on your graphics card .
Its not the vRAM so

99% chance you need to try swapping out your RAM
September 12, 2011 8:27:37 PM

Just tried it with no RAM at all. No effect. Is that what's supposed to happen when you boot a computer with no RAM (fans don't spin, power led turns on then fades out)? if no, then it's not the RAM, right?
September 14, 2011 2:05:21 PM

nordlead said:
I had the same exact symptoms years ago and it turned out to be a combination of PSU and motherboard.


Wow, turns out you were right. I just tried a different PSU with my computer and it worked fine. Then I put my PSU back in and it started but it looked like it struggled to turn on. I turned it off and on again and it wouldn't start.

The funny thing is that my PSU works fine in my friend's computer. So we just ended up swapping. Is my PSU damaged? Can it cause problems in my friend's computer?
September 14, 2011 2:05:34 PM

Best answer selected by lyoshenka.
a b B Homebuilt system
September 14, 2011 2:53:30 PM

lyoshenka said:
Wow, turns out you were right. I just tried a different PSU with my computer and it worked fine. Then I put my PSU back in and it started but it looked like it struggled to turn on. I turned it off and on again and it wouldn't start.

The funny thing is that my PSU works fine in my friend's computer. So we just ended up swapping. Is my PSU damaged? Can it cause problems in my friend's computer?


I would toss the bad PSU, since you never know what it might damage. Not worth the risk unless you really don't care about the PC.
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