First of all, MANY thanks to Gary, Claude, Andrea, Mike , Danb, and vic83, for sharing your advice.
Here's the latest update of my situation. I purchased and installed Ultra WinCleaner (as recommended by Traveling Easy) to remove corrupt, erroneous, or uneeded Windows registry files. Unfortunately, I found the WinCleaner utility to be overly aggressive, as it deleted 532 registry files. After that, I was no longer able to launch my email client: IncrediMail. WinCleaner also has a feature that allows you to selectively add/remove individual registries but even after I reinstalled all registry files with the name 'IncrediMail' in it , I still wasn't able to launch 'Incredi-Mail'. Thank goodness for Windows XP's 'system restore' feature which allowed me to revert back to the computer's settings before I had installed WinCleaner and it's removal of some obviously needed registry files.
In the meantime I have good news
to report. For whatever reason , and which remains a mystery to me, I'm no longer experiencing computer startup problems or the HD error reports I'd gotten previously, and all the Norton Utility diagnositcs tests continue to report back that all my windows files & hard drives are error free and functioning properly. It's been 4 days now running good, so I'm keeping my fingers crossed.
Funny thing now though is that I've still got those 532 windows registry files in my computer that WinCleaner wanted to delete. I just wish I knew how to to selectively figure out myself which ones are 'actually' needed or not.
Scott