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I have two computers: my main one, and an older one. Currently, both are fully hooked up, and neither will respond when the power button is pressed or held. No fans, no lights, no sign at all.

Prior to tonight, both had been running just fine, daily, and there have been no hardware changes for 8 months.

From the beginning: I was gaming away on my main computer, when it shut off. It sounded like it does when the power goes out in the house, but that wasn't the case this time, and it wouldn't turn back on.

Naturally, I tried to diagnose the problem by swapping parts, one by one. I first tried hooking up the old computer's power supply (550 W) to the new computer. There was no difference. So I figured it must not be the power supply. Just to be sure that it wasn't, I tried hooking up the new power supply (700 W) into the old computer. It didn't turn on either.

It was at this point that I returned both computers to their original configurations. Checked all of the connections: 24-pin motherboard, 8-pin motherboard, case power switch, everything.

And now the old one won't turn on either, even though it's back to exactly the way it was.

The only difference between how the two are working right now is that the old power supply (550 W), very rarely shows signs of life - a brief light on the new case, or a brief twitch of the CPU fan on the old computer.

I inspected carefully for any signs of physical damage on both motherboards, but other than capacitors bubbling, I don't really know what to look for.

So, did my motherboard fry both power supplies? Did my power supply fry both motherboards? I have no idea what's going on here. I realize that I was reckless in my part swapping and fried one more thing than I should have, whatever it is. I'm fully prepared to buy three new components tomorrow if I have to.

I would just like to know how I can verify, without ruining anything else, exactly which parts I need to swap out for new ones. I searched other questions but I don't see any with quite the same symptoms. Particularly, I think the old power supply may still be working but both motherboards are junk.

Relevant parts list:

New:
  Gigabyte GA-Z77X-D3H motherboard
  OCZ Mod X Stream Pro 700 W power supply
Old:
  Intel DP55WB motherboard
  Ultra ULT-H550W power supply

EDIT - UPDATE Bought a power supply tester, and used it to verify the problem. The new computer's power supply was completely dead, the old computer's power supply was fine. Bought a new power supply for the new one and it works. The old computer still won't turn on, but at least I'm up and running and can troubleshoot that one at my own leisure.

Thanks again.

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Did you try leaving the power supply plugged in but off for 10 minutes? Some power supplies have a protection circuit which require a "time out" to reset, and you may have tripped it. Also maybe try plugging in only the motherboard+CPU, and seeing if that works, then adding other devices one by one ? Also, its unlikely a motherboard would have fried a CPU. (Not impossible though) –  davidgo Aug 18 '13 at 7:55
    
I have now tried both of those, and neither worked. But I didn't know about the protection circuit; thanks. –  Rick Aug 18 '13 at 8:08
    
Try shorting the sense pins on the PSUs to see if they turn on at all. –  Ignacio Vazquez-Abrams Aug 18 '13 at 8:46

1 Answer 1

It is far more likely that a bad power supply fried both motherboards, than a motherboard fried both power supplies.

Checklist

  • Is the power supply set to the correct voltage (120/240)
  • Have you drained any capacitance?

    Leave plugged into wall (for ground) switch rocker switch off, and hold power button on computer for 5 seconds

  • Have you let the power supply unplugged for 10 minutes?

  • Is this a modular power supply? Remember Modular cables are different between manufactures, and will kill components. See Do I need to replace my CPU or Motherboard, PC not powering on

  • Have you reseated all components (cables, video card, ect..)?

  • Have you tried a different power cord?

  • Have you tried a different wall outlet?


By this point the power supply is more likely than not dead. A few last ditch efforts.

  • If you have a power supply tester, plug it in.

  • If you don't have a tester, but do have a multi miter, check the voltages

Turn PSU on by putting a 10K resistor between the green wire and a black wire. Probe the Orange (3.3v), Red (5v), and Yellow (12V) wires.

If you still see no signs of life, replace the power supply with a known good unit. (Make sure you don't reuse any modular cables).

If you have removed all variables, and the computer still doesn't turn on, it is likely a bad motherboard.

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Thanks for your response. I have tried everything on the checklist except the multi meter, and no luck. I did even replace the power supply with a known good unit (the one that was working on the old computer and now isn't). I'm out of time, just going to pick up a new power supply and motherboard. –  Rick Aug 18 '13 at 16:33

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