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I have been having some strange issues with my PC. Twice a day, the computer will just shutdown – no warning, just an instant black screen power off. Now, all the lights and such in the PC are on, graphic peripheral power is green etc, however pressing the power button just does nothing. After a few hours (sometimes turning off at the wall works) it will magically start working again, no issues in runtime (the bios has reset, however) and well. yea.

In addition to this, it will also start randomly powering on. Just randomly, in the middle of the night, will just boot itself up.

I first thought power supply, pulled out my multimeter and checked all of the 24-pin outputs, all check out fine (with the largest deviation is 0.1V). I checked the PS when the PC was turning on fine and when it was not, pretty much the same values.

So, probably not the PSU. So, unplugged everything, RAM – GPU – HDD/SSDs, still not turning on (and unfortunately I can't unplug the CPU simply because it won't turn on anyway (or will it?) ). I thought maybe thermal issues, but it's' running cold. Even did a bare hand test, flat cold (plus, it would cool down after a few hours, however sometimes it doesn't turn on).

I even went so far to test the waveform of our power to maybe see if that could have made a difference (I was getting desperate), but it's perfect ~50Hz sinewave.

So I'm thinking either Motherboard or CPU. I just want to get a second-hand opinion on this. I was planning on getting a new MB and a CPU to go with it anyhow, but I don't want to go purchase it then realising a) the issues still happening and b) I'll have no left over cash to buy the 'fix'.

I've done a bit of googling around and most people say it's probably the PSU, but the pin values are perfect so I can't imagine it's that. Plus, the PSU it's too old at around ~3 years.

Just to clarify, when I say not turning on, I mean not turning on. No fan spin-ups, no nothing. The only sign of life are the lights on the GPU that glow if it's receiving power or not.

My specs are below (probably not important but still): - Nvidia GeForce GTX 780 - Intel 4440 CPU - Thermaltake Toughpower 750W - Asus B85M-E Motherboard

I was planning to try and boot into Linux the next time it starts working to see if the issue will happen in Linux (could be some gnarly virus causing sustained processor interrupts, maybe.. as I said – getting desperate)

Anyway, any help or opinions would be appreciated!

  • Questions that might help diagnose: 1- sounds like you have it on a power bar/extension/etc, have you tried switching that out yet? 2- does it shut down when you're doing something specific? 3- starts up in the middle of the night -> anything else on that circuit starting at the same time (thinking along the lines of freezer/refrigerator compressor). try plugging it into a different circuit? out of ideas for now... – s1ns3nt Jul 6 '17 at 16:14
  • random power-ups COULD be related to your cmos battery. Have you tried replacing it? – Blaine Jul 6 '17 at 16:33
  • also, have you tried running off integrated graphics (if you have them)? the whole black screen w/ green light suggests a graphics issue – Blaine Jul 6 '17 at 16:34
  • I've replaced the CMOS battery, still getting the same issue. And I don't think it's Graphics simply because it refuses to turn on at all. Currently it's turned on so I can't do troubleshooting, when it next plays up I'll try plugging it directly into the wall and see if that resolves the issue! – Polymer Jul 8 '17 at 2:06
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As @blaine mentioned in comments above try replacing the CMOS battery (I don't have enough points to comment only answer, sorry).

This worked for me today on old MacBook Pro laptop (running Windows 10) that would not power on. It would not POST at all for a day or so, would boot a couple of times and then fail again for hours or days. Very similar sounding to your issue.

A new CR2032 battery from supermarket fixed it immediately.

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  • That's alright! Always annoying being a new user on a different network! I have already tried replacing the battery, however, it wasn't a brand new one. I'll try and get a new one from the store and try that out (also trying the other stuff mentioned in the comments above :) ) – Polymer Jul 8 '17 at 2:52

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