Ubuntu 10.04.1 LTS fails to shut down - Just hangs up computer: SEE QUEST#: 123013 (same problem)

When I click on the upper right panel for shutdown or even when I use a root terminal and type in "shutdown now", ubuntu exits, and then the computer hangs up. I have to unplug the computer - nothing else will do it. Did not have this situation with Kubuntu 8.04 LTS. My machine is an old COMPAQ Deskpro EN.
I wonder if this has anything to do with the initial installation of Ubuntu? I installed the program 3 different times and each time just a background screen appeared with no upper or lower panel. Eventually, on the last installation, the bottom panel suddenly popped up but the upper panel was off the screen. I was able to access the bottom edge of the upper panel and readjust the settings until it displayed properly. I used the 'desktop' CD version for installation. Would the 'alternate' version have worked better? Everything seemed to go well during the installation except for the panels not appearing at the end. Is there something here that might relate to the power-down/shutdown problem I described above?
Thank you for your time.
walt
NOTE: I JUST READ QUESTION#: 123013 WHICH SEEMS TO EXPLAIN THE SAME PROBLEM THAT I AM HAVING! SOMETIMES I GET THE SHUTDOWN SPLASH SCREEN AND IT FREEZES WITH the last two 'dots' still filled in. At other times I see just a white screen flash by then the screen turns dark and the computer freezes up.