AMD XP PC starts automatically... power supply issue?

[Thumper]

My AMD-based XP machine boots automatically (when I plug in the power)
and does not shut down (power off) when I shut down from Windows or
hold the power button.

To be clear, when the computer is restarting and I'm still in viewing
the memory test and other pre-Windows messages, and I hold down the
power button, the computer restarts instead of shutting down.

The only way to shut it down is to put into off mode the switch on the
back of the case, near the power box fan.

I assume there is a problem with my power supply box. Is there a
diagnostic tool to test the power supply? Is this something I need to
replace? Or is this a motherboard issue (Asus A7N8X)?

 

[Noozer]

My AMD-based XP machine boots automatically (when I plug in the power)
and does not shut down (power off) when I shut down from Windows or
hold the power button.

Mainboard or PSU could be hardware issues. Could also be something asserting
the "Wake" signal like a network card or modem, so disable any options in
the BIOS settings that could wake the PC.

 

[Cal Vanize]

My AMD-based XP machine boots automatically (when I plug in the power)
and does not shut down (power off) when I shut down from Windows or
hold the power button.

To be clear, when the computer is restarting and I'm still in viewing
the memory test and other pre-Windows messages, and I hold down the
power button, the computer restarts instead of shutting down.

The only way to shut it down is to put into off mode the switch on the
back of the case, near the power box fan.

I assume there is a problem with my power supply box. Is there a
diagnostic tool to test the power supply? Is this something I need to
replace? Or is this a motherboard issue (Asus A7N8X)?

I've had this happen in the past probably with this particular board. I
can't remember what I did. Try clearing CMOS and trying again.

 

[Thumper]

Now the computer won't boot. The fans start to spin, the hard drive
begins to churn and then, suddenly, there is a click and the the hard
drives go quiet and then start spinning again, and then there is a
click, etc.

On the front of the computer, the green light turns on, as does the
DVD drive light, but then the lights turn off momentarily when I hear
the click.

Is this clearly a power problem? Do I need to bring it to be repaired?

 

[Thumper]

Update: Here is video of the fans spinning and with sound of what I
hear when the computer does not start:

"

 

[Thumper]

Correct URL:

 

[kony]

Update: Here is video of the fans spinning and with sound of what I
hear when the computer does not start:

"

It does seem that your power supply has now suffered
multiple failures, one being a failure to shut down and
another that it's out of spec so it tries to shut down but
can't. I don't guarantee this diagnosis but would be more
confident if you had multimeter readings to monitor the
voltage while this was happening.

Just in case I'm wrong, unplug the hard drives and see if
the problem still occurs, then plug back in and retry it
again. However, if your PSU is going out of spec and not
turning off as it should, it is risky to continue powering
the system with it for anything further.

What make and model PSU is this? Ideally with that
motherboard you'd want a good name-brand spec'd for at least
200W of combined 3V+5V power, and more being even better.