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I recently shut down one of my desktop PCs, moved its power cord from AC power to a UPS, and then tried to power it back on. Much bafflement ensued. It had power (some indicator lights on the mobo), but I couldnt even get the mobo to try to power on much less post successfully until I reset the CMOS. Even the power button on the mobo itself did jack all, so I know it's not a loose cable to the front panel power switch After that, the mobo posted OK and the OS booted without issues. I kept all of the same bios settings (I havent touched these in ~5 years), and some testing shows the CMOS battery to still be good.

Has anyone ever seen this happen? I've never seen a CMOS reset do anything with a CMOS battery that's still good, and literally nothing changed aside from shutting it down and changing the power cable from AC to a UPS drawing from the same socket.

I recently shut down one of my desktop PCs, moved its power cord from AC power to a UPS, and then tried to power it back on. Much bafflement ensued. It had power (some indicator lights on the mobo), but I couldnt even get the mobo to try to power on much less post successfully until I reset the CMOS. Even the power button on the mobo itself did jack all, so I know it's not a loose cable to the front panel power switch After that, the mobo posted OK and the OS booted without issues. I kept all of the same bios settings (I havent touched these in ~5 years), and some testing shows the CMOS battery to still be good. Has anyone ever seen this happen? I've never seen a CMOS reset do anything with a CMOS battery that's still good, and literally nothing changed aside from shutting it down and changing the power cable from AC to a UPS drawing from the same socket.

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[–] • 0 pt

It is possible that your power supply is going bad. I have had very strange behavior from an older power supply that was slowly failing. Things like the system not going to sleep properly or resuming from sleep. Having to hit the power button twice to boot.

Replaced the PS and everything started working perfectly again. That was 6 years ago on the system I am using to type this. (Early gen i7).

[–] • 1 pt

Thanks for the tip. I'll keep an eye on that PSU.