I have a desktop PC that is just over a year old that I use daily for work. It's running Windows 8.1, has 16GB RAM and an i7 CPU. It has a 256GB Samsung 840 SSD (Windows + programs) along with a 1TB Seagate HDD (documents). The motherboard is an ASUS B85M-G. The graphics card is a 2GB ZOTAC GT640, with two monitors attached.

As of Friday last week it is shutting down (without warning) after 30 minutes of uptime. I have not installed any new hardware recently, nor installed any new software (other than whatever Windows updates came along last week).

By "shutdown" I mean that it is as if the power cable was pulled from the PC. Screen goes blank, cooling fans stop spinning, and I can hear a "ping" from the 1TB HDD as the drive head parks.

Initial speculation suggested that this was a classic PSU issue, so I obtained a replacement power supply and plugged that in this morning. Same problem.

While in Windows I have run temperature monitoring software that shows that the CPU cores are happily down at around 40°C, and the GPU is at a similar temperature. The innards of the PC are clean and free of dust, and all fans are spinning.

BIOS reports that CPU temperature, fan speeds and voltages are fine:

BIOS screen

Following a shutdown and restart I've inspected the Windows event logs, but have not found anything that explains the shutdown, only a log entry that says that Windows was not shut down properly.

I have also discovered that the problem persists if I just enter the system BIOS on boot and let the PC sit there for half an hour (so it's not a Windows issue...)

I have upgraded the BIOS since I bought the PC, but this was back in May.

I have checked the RAM using Memtest86+, this reported no issues but sadly was only able to get about 60% of the way through before the PC shutdown.

For what it's worth, there is very little clearance between the heat sink on the passively-cooled graphics card and the RAM. However the heat sink is generally cool to the touch. There is also not much clearance between the CPU heat sink fan and the graphics card, but again temperatures are fine. Photo below illustrates the internals...

PC internals

Can anyone suggest what might be going on here?

Edit - Troubleshooting progress

Since originally posting this question I've tried the following in an attempt to isolate the issue. In all cases the PC still shutdown after 30 minutes:

  • Unplugged optical drive, entered BIOS screen
  • Removed graphics card, allowed to boot to windows (presumably, as I remembered I'd previously disabled onboard graphics in BIOS so couldn't get a picture on my monitor
  • Replaced graphics card with another, unplugged all USB devices apart from mouse and keyboard, entered BIOS screen
  • Unplugged SSD and HDD, entered BIOS screen
  • Removed backup battery for BIOS, waited half an hour, put battery still in. Booted and went to BIOS screen
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    In BIOS, do you have a Hardware/Temperature Monitor? What are the temperatures just before shutting down? – Cornelius Sep 6 '14 at 16:30
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    Have you checked the event logs? – DavidPostill Sep 6 '14 at 17:01
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    Ah, important ones are usually near north bridge, which is covered with your cooling system :( – Basilevs Sep 6 '14 at 17:27
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    How do you define 'shutdown', does the PSU turn itself off, does the standby power turn off as well? And is it after about 30 min, or after exactly 30 minutes? – AVee Sep 6 '14 at 23:03
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    It looks like there are two banks of memory in there, pulling one out and trying again might be a useful test (try both separately). Resetting your bios to factory defaults seems useful, there could even be a shutdown timer in there or some standby issue. And pull the plugs going to your case, power, reset etc. A flaky button could also cause issues. Either pull the plug for the power button after turning it on, or turn it on by shorting the two pins connected to the power button with a screwdriver. And grab a stopwatch, see if it's exactly 30 minutes, in that case it's likely a bios issue. – AVee Sep 7 '14 at 18:15

Problem solved: it was the motherboard.

I obtained a replacement under warranty and switched it out. The original motherboard will be going back to the manufacturer, so if I find out what the issue with it is I will post an update here.

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    (Update: I was never able to find out what the issue was with the original motherboard...) – Richard Ev Mar 6 '15 at 8:09
  • Probably something with Intel ME since if the ME firmware (or more like spyware) isn't found the computer shuts down after 30 minutes – Suici Doga Feb 12 '18 at 12:53

A few of suggestions:

  1. Try booting in safe mode and see if it still happens. That might isolate a malware or driver issue.
  2. It could still be a power supply issue. If the amount of required power is right on the edge of what your supply can deliver, it might be that when you swapped in another [assuming it has the same power rating], it suffered the same issue. Try a power supply with a higher power rating.
  3. I once had a case here the video card was causing the computer to only make it part way through POST before causing a shutdown. Now, that was different, in that it happened after a few seconds and not 10s of minutes like in your case ['cuz a video failure was detected by POST], but who knows. If you're using a video card and your mainboard has it's own video processor, then try removing the video card and plug a monitor into the mainboard video port, and see if the problem goes away.
  4. Capacitors are notorious for this kind of failure. For instance: the bond between one of the leads and the capacitive component comes loose but still makes contact, until it gets hot, where dissimilar expansion causes the lead to fully separate from the component. This can occur in other types of component, as well, but in all cases can be difficult to troubleshoot without the proper equipment [and even with]. A can of freeze spray can be used to locate such a thing [but only if you can reach the offending component] -- use a "divide-and-conquer" approach.
  5. Some ICs have internal thermal shutdown -- especially regulator ICs. Mainboards often have linear regulators and if one of them is heating up, it may be shutting down a critical function. Try scanning the board with a non-contact temperature sensor [or even better a thermal imaging camera]. At around 20 to 25 minutes after power-up, look for devices that are hotter than surrounding devices, then hit them with freeze spray. If the computer doesn't shutdown at 30 minutes, then you have likely found your culprit. Then it's just a matter of replacing the part. BUT, consider that the part [especially if it's a regulator] might be getting hot because something else is drawing excessive current. The possibilities:

    A. It might be normal for the part to get hot, and something internal to the part might have failed, causing it to shutdown at a lower temperature than it's specified to do so. In which case replacing the part would be the best course, or consider option C.

    B. Track down the cause of the excessive current. This will, probably require a schematic, and can be very difficult.

    C. Put a heat sink on the part. This is a "band-aid" approach [like using chewing gum to repair the throttle linkage on a race car], but what the heck, if it keeps you going, then why not! You can get heat sinks with peel-and-stick insulator pads [search on "heat sink" at Amazon, for instance] -- also there are many for XBox and Raspberry Pi GPU]. Look for one with the best fit for the part.

  6. This is a shot in the dark, but I had a similar problem, once, and I traced it to the backup battery.

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    FYI: I did a number of edits after the initial post -- added a great deal more content ;) – ReverseEMF Sep 6 '14 at 19:06
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    As to 5, turn it on, wait for it to turn itself off, then immediately turn it on again. If it's something thermal it either won't go on or shutdown way quicker. If it stays on for 30 minutes again it's not an heat issue. – AVee Sep 6 '14 at 23:12
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    Based on the symptom mentioned in the title (BIOS screen), suggestion #1 (safe mode) is a waste of time and undermines your credibility. – sawdust Sep 6 '14 at 23:49

Try Changing RAM with some other piece of RAM. If you have two 8 gb RAM try both one by one and wait for 30 mins. I also have simmilar problem solved with replacing RAM.

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  • I've checked the RAM using Memtest86+, which reported no issues but only got about 60% of the way through before the PC shutdown after 30 minutes. I have a replacement motherboard and RAM arriving later today, so should know more this evening... – Richard Ev Sep 9 '14 at 10:00

I had this happen to me when the fan of my graphics card broke. I didn't notice that the fan wasn't spinning, so everytime the card got too hot, the PC did shut down without a warning.

But the temperature of the card was well above 100 deg celsius, I just wasn't monitoring that temperature.

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  • Out of interest, did your shut down happen after a fixed period of time, or did it vary according to the load that your PC was experiencing? – Richard Ev Sep 12 '14 at 7:26
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    It did vary, but it didn't happen before a certain amount of time. I think I started to believe that this was an issue with the graphics card when the shutdown occurred more often when watching a youtube video. Then I checked. But this was after about 3 weeks of having this problem. My PC did shut down about three to four times a day, and since it started after a Windows Update, I thought that that was the culprit. Horrible days... – Daniel F Sep 12 '14 at 11:29

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