Strange PC behavior - not sure if hardware or software

My computer has been acting strange. When it is powered off, and I press the power button, turns on for a few seconds, then turns off. 5 seconds later, it turns on again and boots up normally. I am a bit worried, it did not used to do this. Does anyone know anything about this?

Could be overheating. Most motherboards have a failsafe temp that once reached it will shut off. Could be something else like memory also. Do a Memtest and see what happens. check CMOS for temps as you boot up. If all this checks out it could be the PSU.

some motherboards have this feature that when there is a sudden power off that it will instantly turn back on by itself. I have it on my Asus H81M-E and have turned it off I think.

sounds like not stable overclock, did you overclock your PC?

could you provide some system specs?
Would be very helpfull

try to reset your cmos i have had this issue a ffew times. it should work.

No , I didn't

I recommend checking PSU, and also downclock if possible or/and restore default bios/uefi settings.

How to do a memtest?

I fiddled with that before and nothing changed.

Restoring the default BIOS settings fixed it. I wonder what setting screwed things up?

maybe you changed a setting without knowing of what you did. it happens

To me sounds , if it is a recent board, like the bios, mainly a memory checking system or a memory matching system. The you turn on and it turns back of, then back on , is one of these indications.

Most Linux Live DIstro's have a memtest option in grub. if not you can download meatiest and run it off dvd/cd.

Glad you found the problem. If you went into your bios recently you may have changed a setting on accident and didn't realize.

I'm afraid to go back in and reconfigure since I don't know which setting it was.

The computer that I built for my father had this problem. I tried everything I could to nail down why it was doing it, and it turned out that it was doing it when he tried to turn the computer on when his external hard drive was connected, regardless of boot order. So, he annoyingly has to disconnect that before he boots it on.

This was on a Gigabyte LGA 2011 motherboard. Don't remember the model.