Generally speaking technicians do not try to pinpoint the source of the problem because....
I understand. I have spent stints in tech support, and appreciate the limitations of an environment such as this.
1: Run System File Checker.
Have done several times since the reboot problem started. I start a scan without the CD inserted. If a replacement file is needed, SFC will ask for the CD, otherwise the progress bar will run to completion. This tells me whether one or more system file have been replaced.
I still have to find an SFC log that will tell me what was replaced, and better still, which files were checked.
2: XP repair. This is a process that I hardly ever use because many times you end up with more problems then you start with.
I share your reservations, and have some experience of failed repair consequences with systems other than XP. As a general approach, I prefer to track down the cause of a problem, and deal with it specifically.
I thank you, and all those who took an interest, very much for all your time and help. I had no idea of how to even begin to tackle the problem when I first posted it on the forum. Now I understand much more, and have several options to follow.
I am extremely grateful to you all.