I don't know why Norton is behaving differently on the two computers, except that the desk top is old, has windows XP & 32 bit. The laptop has windows 7 and is 64 bit.
Although the desk top is currently connected to the internet via my ISP, whenever I try to access any of the Norton features I get the message that IE cannot display the page as I'm not connected to the internet :-/
After trying various things all evening and not getting anywhere, a Norton window appeared that said there was conflict with a proxy server. Norton is currently scanning and hopefully sorting out whatever problem is present. Can't think why this problem has suddenly occurred as the proxy setting mentioned in my first post has always been there.