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I'm looking for some diagnostic advice.

computer was assembled 2 years ago, no issues since.

symptoms: computer randomly loses power (usually happens in 2's. IE computer suddenly loses power. I restart it, a few minutes later it shuts off again, then no issue for a day or 2.)

what I've tried already:

there is no event log for the power loss, only a post restart event saying that the last shutdown was unexpected.

all system temperatures are well below normal (30-40c) although the graphics card seems to be around 75c which is still well below the maximum running temp or 98c.

hard drive checks return healthy.

I'm not sure how to even diagnose whatever else could be the issue (uneven electrical from the socket, power supply going bad, cpu burning out).

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  • one (of many) things it could be the pannel switch on the case, People got liquid in them before and it would operate itself oddly, If i had such problems i would look closely at the motherboard , to see if any components were looking different.. You could smell your PSU , if the PSU is one with very low air flow, you could change that somehow, check the fans to see if all are moving, and dust.
    – Psycogeek
    Commented Mar 30, 2015 at 17:32

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If you've verified it's not overheating, then power is definitely your problem here. It's going to be one of the following:

  • Power from the wall (or power strip) is flaky.
  • Your power supply is bad.
  • Your power supply is good but too small to handle the load on the machine (you generally see this with cheap no-name power supplies).
  • You have a loose wire or connector somewhere inside the computer. Check the main 24-pin power lead to the motherboard and the 4-pin CPU power lead. Verify all the wires are secure and the connectors are seated properly.
  • The power button itself could be flaky (might be getting stuck closed like you're holding the button down). Check to make sure that's secured to the motherboard and not shorted out anywhere.
  • USB ports could be drawing too much power from the +5V line. Check all the USB port headers on the motherboard and disconnect all USB bus powered devices to see if the problem goes away (this speaks to the point above about the power supply being too small to handle the load).
  • The motherboard itself could be bad in a myriad of ways too.

No matter how you slice it, this definitely sounds like a hardware problem to me. Happy hunting to find it :-) Honestly though, I'd look to the power supply first.

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Apart from the temperatures, which you say are normal, voltages are important too. Check if the monitored voltages are in range, and even when in range, if they don't vary too much. They should be within 5% of the specified value (eg. the 5V line should be within 4.75 and 5.25V) If they do vary, check the power connector(s) to the motherboard. Unplug/replug them and check if the voltage changed at all (of course, shut off the PC first :) And I'm assuming you are talking about a desktop computer, of course).

I assume you do not have a UPS. Some computers are very good detectors of short power-cuts. This might come from heavy equipment on the same line, eg. air-conditioners switching on/off.

One diagnostic: borrow an UPS and use it for a couple of days. That way, you can eliminate the power source as problem source. Also, UPSs generally beep if there is a micro-power cut...

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