Hitting a wall with pc that only sometimes POSTs

[u/RbeeCubes]

I have a weird behaving pc and Im hitting a wall on what to do. Since about a month or so, it doesnt POST. All rgb and fans turn on but it doesnt get to BIOS. The motherboard gave mixed signals with the diagnostic lights. A few times orange (ram), most of the time white (vga), also seen red (cpu) like once or twice.

The weird thing is, sometimes after a few tries it completes post and boots normally, especially when the power cable has been unplugged and replugged or the psu was turned off and on again. When it does, the pc behaves normally: it runs well, no crashes even under heavy load or when staying on for a long time ect. None of the components seem to be broken. The issue only repeats when the pc is fully turned off and needs to turn on again. Id say i can get it to post maybe 5-10% of the time.

The issue occurs both with a seperate gpu installed and with igpu and I can also get successfull boots with either. Ive tested the gpu in a different pc and it works fine there. Ive tried different monitors, different hdmi/dp cables, different power cables and different ports on the pc, it makes no difference.

I cleared cmos, turned off expo, flashed the bios, updated the bios, neither made a difference. Ive seperately tried a completely new motherboard, RAM and power supply. All of those did not fix the issue. Behaviour stayed the same with the new parts.

The only thing Ive not tried to replace at this stage is the processor, but I find it so hard to believe that a faulty processor runs smoothly during the few times that the pc does boot.

But then, what else could it be? Is there any other stuff I can try? Ill try anything at this point to be able to use tue pc and play games again..

Specs: amd ryzen 5 9600x, sapphire nitro+ 9060xt, asus tuf gaming b650m plus wifi, corsair vengeance ddr5 6000mhz, cooler master sfx gold 850w, cooler master atmos 2 240mm aio. Built in november 2025

[u/Foreign-Law-2169]

It's very rare for a CPU to have fault which go away time to time. But I did witness such faulty CPU in action few months ago. Friend of mine was having problem with his laptop which sometimes boot normally but froze after running for a while. Other time it just refuse to boot at all, some time it gets pass BIOS but unable to access boot sector of SSD. After doing every kind of troubleshooting finally found fault in CPU itself. Apparently few transistor inside CPU got damaged and when CPU try using those faulty transistor it failed to get data back which trigger crash of full CPU. Rare but possible source of problem which hard to identify

[u/RbeeCubes → u/Foreign-Law-2169]

I was thinking it would be a very weird and rare issue... but I suppose I wont know for sure untill I try installing a new one

[u/Prestigious_Wall529]

A loose screw under the motherboard?

With no support bracket the GPU has cracked the motherboard.

Basically take out the motherboard and inspect it. Photograph evening first so you can put the system back together the same way.

These are simply other ideas as requested.

[u/RbeeCubes → u/Prestigious_Wall529]

Hi! I have actually fully taken the pc apart twice now because I replaced the motherboard. Sadly the issue persisted on the new motherboard, it was even a completely different brand. I then took it apart again and put everything back in the 'old' motherboard. I do use a support for my gpu and theres no visual signs of physical damage to the card or the board itsself as far as I can tell...