Any help with this would be appreciated; I've asked a techie friend for some help but to only partial avail.

About a year ago or so, my computer stopped being able to turn off completely.  I didn't notice it at first because I used to just leave the thing on all the time.  I wasn't terribly power conscientious, but one day, I noticed that turning the computer off (either from within Windows or by holding down the on/off button on the front of my tower) didn't cause the power SUPPLY fan to stop or the hard drive LED in the front to go out.   I also didn't do anything about it.

Then, a few months ago, my computer started turning on and off randomly.  Holding down the on/off button would have no effect either way, and the computer would turn back on of it's own volition.  I took it to my techie friend and he said it was a power supply problem, probably a combination of the FACT that my power supply stays on even when I turn the system off and the fact that my surge protector is out of date.  It's most likely been exposed to a few power surges unprotected.  So we replaced it with a spare that he had lying around.  However, even after replacing it, it still had the weird issue of not turning off even when the computer is SHUT down.  He checked the BIOS to see if there were any settings that were wrong, but he said it looked fine.  Of COURSE, turning off the switch on the power supply still turns it off, so he told me to just do that whenever I wanted to turn the computer off, after I've shut everything down.  He said the issue might be a problem between the power supply and the motherboard not being able to properly communicate.

Now, my computer works fine (just over six years old), but I'm wondering if anyone knows of something I can do to iron out this issue, so I don't have to wait for my PC to shut down and then reach into the back to turn off the PS (short of buying a new motherboard.)  Has anyone else seen this problem?  Does my friend's prognosis sound right?

Here's some of my computer's pertinent specs:

Manufactured by vpr Matrix, inc. (affiliated with Best Buy)
Windows XP Home Edition (Service Pack 2)
Pentium 4 CPU 1.8 Ghz
1 GB of RAM
Antec Basiq 350 watt power supplyWill it shut down in the safe mode?I just tried shutting it down from safe mode.  As before, the computer shuts down, but the power supply and hard drive lights still stay on.In the bios settings [power mgmt] look for a wake on lan sselection if enabled disable it. Thanks for helping me so far, xavier.

In my BIOS settings, I have the following options and settings:

After Power Failure      [Stay Off]
Wake on PME              [Stay Off]
Wake on Modem Ring  [Stay Off]Leave  it that way on all 3 . I would set the BIOS at best known config. or if your bios says set at default. Is this PC a home build?The PC is manufacturer made, but I've upgraded it a few times (to 1024 MB of RAM and a graphic card upgrade.)

I've set the BIOS to default.I had this problem last year with one of my other computers.
All I did was System Restore to a date before the problem.

Is that possible with you?