Thanks for your ongoing help and patience as I work through this issue.

Your comment to do a clean install triggered an idea. I did a system search for ‘avast’ and found the remnants of previous installations and deleted them.

Then I downloaded a new copy of avast via cnet ( as the avast download page came up with a 404 ).

While XP was shutting down it installed 8 updates/upgrades. I am assuming these were for avast.

The system ran for about half and hour fine until it BSOD with the below screen

More in a minute as it died again