I write this in case anyone else has similar problems. I am aware that XP is out of date and not sure if the problem exists in other operating systems. Also, so that perhaps someone at Norton becomes aware of the cause (or what I have found to be the cause) of an extremely annoying system problem which has occurred consistently on two of my pc's which are running different programs and different versions of Norton anti Virus.
Symptoms: For well over the last year and possibly two years both of my pc's systems would just freeze explorer (not IE but explorer.exe) although some programs continued to work, the ability to shut down the system, run the task manager and many other functions became unusable. I noticed this as they manifested a problem in my email program display every time. These hangs would occur on both pcs about twice a week and usually within an hour of each other. I assumed that it was caused by some program which was installed on both pc's which had a scheduling of some sort which I could not track down.
Finally I stumbled upon the fact that Norton had installed in its directory four files which belonged to Microsoft Visual Studio 2015. The four files were msvcp140.dll, vccorlib140.dll, vcruntime140.dll and concrt140.dll. The versions of these file (in my case were 14.0.24123.0. as it happened, I compared these file versions to those in my system32 directory and found them to be older then those installed in my os. My latest files were vesion 14.0.24215.1. In other words the files being provided by Norton were not the latest files from the vcredit.exe file. By turning off self protection and disabling NAV for a minute I was able to replace the older files in the Norton directory with copies of my files from the system directory, turned back on self protection and re started the computer.
While I can not be sure the problem will not re-occur, so far it has not and I am hopeful. I need to assume that Symantec has a schedule for certain updates which may have been causing the problem and that the schedule was fairly consistent as most of my problems occurred every Tuesday and Thursday usually in the afternoon.
Hopefully if anyone else has the same weird occurrences this information may help.