Dead PC

[surveyor]

My PC won’t turn on.

Initial symptom was it turning itself on. I unplugged it and found when I did plug it back in it had forgotten its BIOS settings.

It’s been off for a while and on trying to turn it on I get nothing.

I have a power light on the motherboard. But no sign of any reaction to the power button.

I have tried jumping the power switch pins.
I have reseated the motherboard power inputs
I have reseated the RAM
I have tried unplugging all other peripherals from the motherboard.
I have tried a bios reset

I am now thinking it is either motherboard or power supply. Neither seem an obvious fault as there is power to the motherboard

I am stuck.

Any ideas?

[Digger]

I would try a spare or borrowed power supply initially - cheapest option.

Power light on the mobo can still mean a failing PSU

[Big_Dog]

Might be a plan to replace the bios battery then check it can still see its boot source.

[Digger]

What is the basic spec of the PC?

[surveyor]

Big_Dog said:

Might be a plan to replace the bios battery then check it can still see its boot source.

Should have said that I have replaced the battery...

[surveyor]

Digger said:

What is the basic spec of the PC?

Asus Strix Z370 MB
16GB DDR4 RAM
I7-8700K CPU
EVGA Geforce RTx 3080 10Gb

[Farmerpalmer]

Is it overcooked?
Try one stick of ram or different ram.
I have had ram failure on a overcooked Asus board

[Mr Pointy]

Is it a standard ATX PSU? If you have a voltmeter to test it you can force it to turn on by shorting pin 16 to ground.

https://en.wikipedia.org/wiki/ATX

[surveyor]

Farmerpalmer said:

Is it overcooked?
Try one stick of ram or different ram.
I have had ram failure on a overcooked Asus board

Not at the moment..

I have had historic problems with a failed water cooler connector. That has been fixed, but I am wondering if the MB / or Power Supply are affected.

[surveyor]

Mr Pointy said:

Is it a standard ATX PSU? If you have a voltmeter to test it you can force it to turn on by shorting pin 16 to ground.

https://en.wikipedia.org/wiki/ATX

Good plan.

[Steven_RW]

surveyor said:

Mr Pointy said:

Is it a standard ATX PSU? If you have a voltmeter to test it you can force it to turn on by shorting pin 16 to ground.

https://en.wikipedia.org/wiki/ATX

Good plan.

I thought he said he had tried jumping to the mobo power pins at the top in the OP.

I have multiple spare PSUs from corsair RM850x and corsair HX1000 and so on if you want one from a known home. I've been meaning to sell them but never bothered. I even have one boxed sitting next to me. But this isn't a for sale site! :-)

[surveyor]

Still dead. I used the paper clip trick to get the fans running so I think it looks less and less like the power supply.

There are some reports that depowering the board completely for 24 hours has an effect. I’m going to try this although not holding out much hope

[Digger]

Could still be the PSU.

[130R]

Have you unplugged everything, including all peripherals/SSD's/GPU, and just tried one stick of ram? (make sure you are using the right slot for single stick ,try one and, if that doesn't work, try another one)

If it still doesn't work you know it must be either PSU, mobo, or CPU. Narrowing it down from there isn't very easy unless you get some kind of code/beep from the mobo or have a working part you can swap in for each of those components to test.

[speedyman]

There will be more than one voltage from the psu. You need a voltmeter to check all voltages are there if you don't have a spare psu.

[surveyor]

Progress. Packed the PC to take to a mates house for him to have a look. He plugged it in and it worked.

Came home plugged it back in and it worked.

So frustrating.

Theory 1. Power wire was loose and I did not check. Can't be sure - I think I checked...
Theory 2. I like this one.. The Bios settings were being forgotten and I had changed the CMOS battery. My theory is the battery was not quite in position and moving it jointed it into place. Bingo everything works. It's a theory at least...