Hi Jimmy,
Taking your points in order:
OK, I will post again when we have closed this issue.
Problem resolved; however, for your info, it turned out to be a problem caused by my ISP changing the way I receive their signal because of a conflict between their servers and my Netgear WiFi Router v7. This resulted in a change of IP address, which the computers picked up dynamically, so I didn't notice for internet access, but the firewalls were blocking the network connections until I entered the new trusted addresses.
OK, I have downloaded Comodo and will install later today. I'm off out now, so will let you know how it works, probably tomorrow after I have used the PC for a bit. I will switch off the XP Firewall as well.
Regards,
Philip