Power On/Off via the Power Supply Button

Updating the BIOS is impossible since I already have the latest version.
(And anyway, from what you’re telling me, it has nothing to do with my problem)

The other PC is even older. Its components are not compatible with this one, except for the burner, the hard drive, and the graphics card. However, I know that the problem is not related to these components since I already unplugged them from the power supply before turning it on to test the power button independently of what was connected to the motherboard. The result was inconclusive, whereas with the other PC, the same operation allowed me to control the power supply with the power button.

So the only remaining suspects for the malfunction are the motherboard, the processor, and the RAM.
I cannot test the processor or the RAM, as they are incompatible with my other PC.
Having 2 RAM sticks installed, I retested by alternately removing one and then the other, with no success.

The RAM hypothesis seems unlikely to me.
The processor hypothesis also seems doubtful. I would be surprised if it had an impact on power management.
Moreover, if it were the processor or the RAM, I should encounter issues while the system is running, which is not the case.

Lacking certainty, I must therefore settle for a strong probability of a malfunction of the motherboard.
Since this does not prevent the PC from functioning once started, I will continue to use the OFF button on the power supply to turn off the PC, the ON button on the power supply, plus the reset button on the case to turn it on.

It's not worth changing the motherboard (which is less than 6 months old), considering that the other components are already quite aging.
When I have a bit of money, I will buy a new PC.

Although it’s not perfect, I will thus conclude that the problem is resolved.

Thank you very much Janos for your assistance and responsiveness.

First of all, thank you for the quick response.

Unfortunately, I don't have another PC on hand to test the power supply.

I haven't attempted to update the BIOS yet.

The problem occurs both when I shut down Windows and when I turn on the PC (via the ON button of the power supply - I have to reset afterwards to start booting).
That's why I don't believe it's an operating system issue.

Just a small clarification: after changing the power supply, the BIOS returned to its default configuration. I have therefore reset the old parameters. Did I miss something?
In other words, can a wrong setting in the BIOS be responsible for poor power management?
Should I consider a chmod?

Absolutely. I did a clear CMOS, without success.
But the problem seems to come from the power supply.

Indeed, I went to the Corsair website, and in the FAQ dedicated to power supplies, there is this type of problem mentioned.
http://www.corsair.com/faq/default.aspx#Q10
So I can't be the first in this case.
They offer a procedure to check if the power supply is defective.
I did this procedure, and the power supply is indeed defective.
Only solution: return the power supply.

I hope I'll have better luck next time.
This is already the second faulty power supply I've bought fresh out of the factory in 15 days.

I will leave a post to update on what happens with the next one.

In the meantime, thank you for your assistance.

Hello,

Continuation of the adventure:

I just tried a power supply that works very well on another PC and, on mine, it produces the same results as before: impossible to turn off the power.

The problem clearly does not come from the power supply.

There is no option in the BIOS to change the PC's behavior depending on whether you press the Power button briefly or for an extended period. However, pressing and holding the power button has absolutely no effect.
So I changed the power options in Windows to see what it would change:

In "when I press the power button" I set it to "sleep"
Result: indeed, if I press the power button, the PC goes to sleep. If I press the same button again, the PC wakes up and the desktop displays normally.

I then reset it to the initial mode:
In "when I press the power button" I set it to "turn off the computer"
Result: Windows shuts down properly, the hard drives stop working, the USB is no longer powered, BUT the power supply does not cut off, the CPU and graphics card fans continue to run, and I can even open and close my DVD drive. Moreover, the power and HDD LEDs remain lit (green).
If I press the power button again (either briefly or for an extended period), nothing happens. I then have only 2 options left: cut the power using the ON/OFF button located at the back or restart the system using the RESET button.

The problem is exactly the same if, instead of pressing the power button, I go through the Start menu to shut down the computer.

I remain attentive to any response that could help me progress, as I am really stuck right now.

Thank you.