My wife's desktop computer is re-booting intermittently. This can occur at any time, during any program.
It may occur immediately after startup or while using Email or while surfing the web. I suspect a possible
power supply failure but would like to hear from some experts about this.

Any help is appreciated.

Thanks

Windows XP SP2
1G RAM 2.6 MHz
80 G HDDYou should start by disabling the automatic reboot on ERROR feature that is on by default in XP. This way we can have a look at any blue screens XP might be hiding.

Right click my computer and select properties
Select the advanced tab
Press the Settings button in the Startup and Recovery frame
Uncheck "Automatically restart" and leave the menus with OK.

Now (hopefully) the computer will give you a blue screen error MESSAGE instead of restarting.
Write down the STOP error code and any filenames mentioned on the blue screen and post back the info.
Here is an example of a blue screen.


Thank You Deerpark for your help.

I did as you suggested, unfortunately a BSOD NEVER did show up to give a clue about what might be happening.

After a couple of days, the computer would not start at all, no fans etc.
I replaced the power supply and all of the fans would operate but still had
a black screen, no video. Also, no beeps were happening during start up.
My son suggested that EITHER the CPU or motherboard were bad.
Fortunately, I found an exact replacement motherboard and an only slightly
slower CPU on line. I have installed those and my wife's computer is now up
and running. I'm really proud of having been able to ACCOMPLISH this as I have never replaced a motherboard before!

Thanks again for your help.

P.S. Is there any way I could test to see which of the old parts is bad, the CPU or Mb, outside of the now working computer?Well I didn't really do much, seems like you managed to fix it on your own.

Regarding the old parts. You can't really test the parts without putting them in a running computer.
You could install the old CPU on the new mobo. If problems resurface it's the CPU, if not it's the mobo.