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My computer has been running fine for 4 years, but yesterday it starts to exhibit odd behavior:

After I shut down the computer, the CPU and GPU fans start spinning at full speed (everything else seems to be turned off). The only way to stop the fans is to cut power by switch on PSU.

Now, if I turn on power by PSU switch, there are two scenarios:

  • If I left computer without power for longer time (like for a few hours), all fans (even PSU and case fans) now start spinning at their lowest speed, case LED is on, I can operate DVD drive, ... but motherboard itself seems to be turned off (onboard display is off) and I cannot turn on the computer by case button.

  • If I switch PSU power off / on quickly, only the CPU and GPU fans start spinning at full speed, and I can turn on the computer normally by case button. After the computer is turned on, fans immediately slow down and everything is OK.

I checked the cables with no results. I also inspected components visually (for things like failed capacitors) - everything seems fine.

I have no idea what component might have failed. Could you please help me?

Specs:

  • Windows 7
  • no overclocking
  • CPU: Intel Core i7-860
  • MB: Intel DP55KG
  • GPU: Sapphire AMD HD 5850
  • PSU: Enermax Modu87+ 500W
  • Case: Fractal Design Define R2
  • case fans are connected to motherboard (not PSU)
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  • What temperatures are CPU/GPU running before you shutdown and the fans start spinning? It could be that you have insufficient cooling (or a problem with your mobo). If you leave them running, do they shut down after a few minutes?
    – Jakke
    Commented Jul 1, 2014 at 13:57
  • I do not think this depends on CPU/GPU temperatures, it happens even if I left computer turned off for hours, turn it on and immediately turn it off. I left the fans running for a few minutes, but they did not stop.
    – novakp3
    Commented Jul 1, 2014 at 14:07
  • Hmm, I tested it again, this time with more patience. The fans slowed down to their lowest speed after ~12 minutes, but they did not stop completely - even after 25 minutes of waiting. When I wanted to start the computer, the first scenario from my question happened, I had to resort to switching off/on PSU, and then the second scenario happened (and I could finally start the computer).
    – novakp3
    Commented Jul 1, 2014 at 14:47
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    try updating your bios. if it keeps happening, get yourself a new mobo
    – Jakke
    Commented Jul 1, 2014 at 14:52
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    If you are shutting down your computer, it does not make sense, for your CPU and GPU fans to be running. Are you sure your not going into some other power state?
    – Ramhound
    Commented Jul 1, 2014 at 15:06

2 Answers 2

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Follow-up: The PSU was faulty. Even while turned off, it supplied 12V to motherboard. I have replaced it, and now everything works as it should.

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  • You should mark this as the accepted answer as it may be useful for others.
    – Jason Bristol
    Commented Aug 20, 2014 at 15:08
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My computer also did this and I solved the problem by replacing the PSU. Mine had similar symptoms: whilst shutting down, CPU fan speed increased and continued to run. The power button stayed lit. I don't want to speculate about whether the PSU was underpowered (it was only 185 watts). However, when I replaced it, I used a 300 watt unit. Now it shuts down normally, which indicates that the original PSU was the cause.

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  • @JakeGould The gist of this post is that in Jabez' experience, the PSU was the problem. While the phrasing of the post may lead you to believe it is purely a comment, there is informational value here sufficient for a regular answer post, in my opinion.
    – Brad
    Commented Nov 30, 2014 at 1:25

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