PC Keeps Rebooting After Shut Down - Windows and Linux - Solved

I have an older HP 8000 Deskpro and whether I ran Windows (any version) or Ubuntu Linux, after powering down, the computer would automatically reboot. I tried resetting it back to the default settings in the Bios and nothing solved the problem.  I also tried disabling the LAN wake settings without success. Nothing worked, until I tried the following:

I then read a thread on an Ubuntu forum, and someone suggested the following:

1- Power down the computer, and unplug the power cord.

2- Remove the cover and remove the CMOS Bios battery (disc) off the motherboard (see below).

3- Wait 1 minute, then re-insert the CMOS Bios battery back into the motherboard. Put the cover back on.

4- Connect the power cord and restart the computer.

5- During start-up none of the old computer's settings will be saved. So you will have to reset the time, date, and then apply the Default Bios settings. Save your configuration and Exit.

6- The problem of rebooting is solved ! Awesome !