Big Red 'L'
I've used all version of Norton Anti-Virus for a long time on several different OS with no problem, I haven't used their total security package though. It sounds as though another security programme maybe interfering, is that possible? ZoneAlarm Pro and Norton work well together so I doubt it is ZAP.
If you have the CD ROM for your OS you can run that and it may come up with a 'Repair and Replace' function, (depends on your OS), this could cure a problem once you have uninstalled any programmes likely to conflict, (trying to do the same job). I am using WinXP Pro with a fairly fast Dell and I can run the OS repair feature in less than fifteen minutes, you then have to go back to 'Updates' and reinstall them.
Have a good look at the programmes you are running and delete any of the little freebees that might be in conflict, suspend any big ones.