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I run an Ubuntu/Windows 11 dual boot system with an AsRock Z370 Pro 4 Mobo which was running fine until 2 days ago. Then, I updated Windows 2 days ago and my computer refused to post yesterday (can't even get into BIOS). I didn't do anything else to the computer (I didn't move it and didn't install new hardware etc.). The computer is about 4 years old and wholly cleaned from dust.

More specifically the following happens: When I turn the power supply off and back on and then press the power on button the CPU fan starts spinning for about 0.5s and then the system shuts down. If I press the power on button again nothing at all happens. When I turn the power supply off and on again I can get the CPU fan to spin again for 0.5s for the first time I press the power on but not for any subsequent presses without turning the power supply off and on.

Yesterday, I removed the CMOS battery for a while and cleared the CMOS and after that, the system posted like normal and I could use my computer. I booted the computer 3 times yesterday at different times of the day (Ubuntu/Windows/Ubuntu). Today, it's again not posting, with the fan turning on for 0.5s.

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    In 99.9% of the cases, the software upgrade is not related to "can't even get into BIOS". Even the success after removing the battery may be incidental. My first guess would be some flakey hardware (that sometimes work, and sometimes doesn't).
    – dirkt
    Oct 23, 2022 at 9:08
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    Unless Windows Update installed a firmware update (for example on Dell laptops), it's just a coincidence. // Maybe try replacing the battery. It really should not cause this behavior, but who knows.
    – Daniel B
    Oct 23, 2022 at 9:15
  • Yes, it's maybe just a coincidence that it occurred after a Windows update. But it actually did not reboot immediately after the Windows update was installed which makes it likely that the update changed something. Changing the battery didn't help. also today clearing the CMOS doesn't help and I can't get it to post at all
    – Corvin Paul
    Oct 23, 2022 at 10:19
  • I agree with @Daniel B, CMOS battery issue should not exhibit these symptoms; however it is worth trying a new CMOS battery as a potential quick fix. Most likely there's a bad component somewhere. You likely unplugged it from the mains electricity when you removed the CMOS battery which allowed it to work again. Try unplugging it again and do nothing else. Check all chips and cards are seated correctly (RAM, Video, etc.) Maybe take them out and then put them back in again, in case something is loose. Could be static building up while it's left plugged in.
    – mark2017
    Oct 23, 2022 at 10:30
  • I took out the graphics card, wifi card, and hard drive, and I unplugged the chassis fans, took the RAM out put it back in, and changed the CMOS battery. Still getting the same result
    – Corvin Paul
    Oct 23, 2022 at 11:10

1 Answer 1

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It turned out that the power supply was not working. You can test your power supply using this guide https://www.evga.com/support/faq/faqdetails.aspx?faqid=59582, or even better borrow a PSU and see whether it's working with the other power supply.

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