[SOLVED] PC won't turn ON unless the PSU switch is turned OFF/ON first.

Jan 25, 2022
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I built my PC about 2 years ago and haven’t had any issues until now. The problem started when I got back from being away for a week. I pressed the power button on the PC and nothing happened. So I turned the PSU power switch off and back on, then pressed the power button and the PC started perfectly. Once it’s running, everything works normally and there’s no issues. But any time I shut down the PC, it won’t start up unless I cycle the PSU power switch off/on first, then press the power button.

I also noticed that if I cycle the PSU switch off/on, then wait about a minute, the computer will not turn on when I press the power button. I have to cycle the PSU switch off/on and then press the power button right after, then the computer starts up fine.

What I’ve checked:
  • The cable between the power button and the mobo (no issues)
  • I removed the power cable and jumped the PWR pins on the mobo and the computer did not start. So I don’t think it’s an issue with the cable or the power button.
  • I checked all the power cable connections from the PSU to the mobo etc.
  • The mobo doesn’t appear to be shorting on the case. The mobo mounting pins all look fine from what I can tell.
Hardware:
  • Intel i9 10900K
  • Asus ROG STRIX Z490-E mobo
  • Corsair RM850x Power Supply
  • Corsair Vengeance RGB Pro 32 GB (4 x 8 GB) ram
  • RTX 3080 GPU
  • Phanteks Eclipse P500A case
Is this just a failing power supply? If so, I’m surprised because it’s a decent quality Corsair PSU, and I haven’t overworked this computer at all. The computer only gets light usage.

Or maybe it’s a mobo issue, or something else?

It’s interesting how consistent the fix is. Just cycle the PSU switch off/on, then it starts perfectly each time.

I’m planning to start by getting a new PSU and putting that in, but wanted to get any thoughts here first.

Thanks for the help!
 

Karadjgne

Titan
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Ohh. Yes, that's a possibility. 95% of those power bars are useless as anything more than a splitter. Just 3 strips of thin metal in a plastic housing. Any 'surge' protection is a 10A or 15A breaker, same as what's in the house breaker panel. They really don't do anything to protect against voltage surges, they only protect you from pulling too much amperage through that particular wall plug. If you have a TV, clocks, phone chargers, lighting or other things using that same circuit, that's all on the house breaker, and adding the power strip doesn't affect them. You could still plug in enough to pull the full 15A into that strip, and have more besides, overloading the entire circuit.

You'll have to experiment with the pc either on a different power strip or simply without one to eliminate that possibility.
 

Karadjgne

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Sounds like for some reason a protective circuit is engaging. It takes a reset by psu power off/unplug to disengage the protection.

I'd check the voltage at the house outlet, hot-ground should be @ 120v, hot-neutral should be @ the same, neutral-ground should be 0v. If there's voltage on neutral-ground, it's possible the psu is picking up on that when there's no load. A fast reset of the psu might avoid that long enough to apply a load, but a long reset will engage the 5v rail to power USB and put the psu into Standby mode, tripping the protection and not allowing power up.

If voltages are good, I'd suspect your psu might have received a power spike and now be faulty.
 
Jan 25, 2022
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I'll have to dig out my voltmeter and test the outlet. I did try plugging the psu into a couple of other outlets around the house, but that didn't help.

The PSU has always been plugged-in to a Belkin power bar with surge protection, but maybe it still got hit with a power surge somehow?
 

Karadjgne

Titan
Ambassador
Ohh. Yes, that's a possibility. 95% of those power bars are useless as anything more than a splitter. Just 3 strips of thin metal in a plastic housing. Any 'surge' protection is a 10A or 15A breaker, same as what's in the house breaker panel. They really don't do anything to protect against voltage surges, they only protect you from pulling too much amperage through that particular wall plug. If you have a TV, clocks, phone chargers, lighting or other things using that same circuit, that's all on the house breaker, and adding the power strip doesn't affect them. You could still plug in enough to pull the full 15A into that strip, and have more besides, overloading the entire circuit.

You'll have to experiment with the pc either on a different power strip or simply without one to eliminate that possibility.
 
Jan 25, 2022
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Thanks for the great info Jaradjgne! I tried plugging the psu directly into a few different wall outlets (without the power bar) but it didn't make a difference. The case power button doesn't do anything unless the psu power switch is cycled off/on first.

One thing that might be worth mentioning is when the PC is turned off, and the psu switch is on, the mobo appears to have power. I can tell because the RGB lights built into the mobo are on. This has always been the case when I shut down the computer, the mobo RGB lights stay on.

So even though the mobo seems to have power, when I press the case power button, nothing happens. I always have to cycle the psu power switch off/on first, then the computer starts using the case power button.
 

Karadjgne

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The pc is never 'off' unless you hit the switch in the psu. There's a difference between Standby mode, which the leds, usb ports, etc are still active and 'On' where the OS is active. It's just like a TV, it always has power (the power button and remote active circuit) unless you unplug it. Just because the screen is off doesn't mean the TV is off, or there'd be no response when you hit the button on the remote.
 
Reactions: Jo_Hardy
Jan 25, 2022
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Thanks Kardjne! Well, hopefully, it's just a faulty psu. I ordered a new psu and it will arrive next week. So fingers crossed that will fix it. I'll let you know.
 
Jan 25, 2022
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I installed a brand new Corsair HX1000 last night, and it made absolutely no difference. So I've spent $300 CAD on a new PSU and the exact same problem still exists. 😭
 

Paperdoc

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My first thought was that is a LITTLE like a problem I had years ago, but not exactly. That WAS a failing PSU. You already have proven that is not your cause - a new PSU made no change.

Did I get this detail correct? I think you say that the failure to respond can be solved (temporarily) by turning OFF the switch on the back of the PSU for a short time, turning it ON again then QUICKLY pushing the front panel power button. You do not need to leave the rear switch off for a long time. Further, if you do wait for a while after it is turned on, it still fails to respond to the front button push. Correct?

If I got that right, this certainly appears to be a problem on the mobo. But exactly what the cause is escapes me.

You mention that "RGB lights" on the mobo are lit when not running - not uncommon. I presume you mean the "Strix" and "ROG" displays. But there are also three diagnostic indicators on your mobo that can provide info. See your mobo layout and key on p. 1-2 and 1-3, items 20, 21 and 22. See also manual p. A-1 to A-4 for all the codes that might be displayed on the QCODE unit at bottom edge near the rear. (Info on how to interpret the other two sets of lights is not there.) That code displayed on that QCODE unit may help you find a problem. Make note of any info there AND on the two other diagnostic light systems in FOUR conditions:
(a) when the system is connected to the wall power and has been shut down and will NOT start up again;
(b) immediately after you have cycled the rear power switch off / on but NOT pushed the front button;
(c) after you have done that but WAITED for a while so it still will not start up; and,
(d) after you have done your full process with a quick re-start so the machine is running normally.

Post back here just in case someone DOES understand all that info and can help - it won't be me. But ALSO contact ASUS Tech Support for help to understand what those diagnostic displays mean.

A last thought about mobo mounting stand-offs. A mistake there can cause intermittent short circuit problems. Most mobos have nine mounting holes in three rows of three. The design intent is that there should be a standoff under each of those holes to space the mobo away from the back plate of the case, but support it at those points. So there should be a standoff under each hole. More importantly, there should NOT be a standoff under the mobo at ANY location where there is NOT a mounting hole. The screws that go through those holes into the stand-offs are supposed to Ground the mobo at those nine points. But there NEVER should be a Ground contact point on the back of the mobo anywhere else.
 
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