I've been hosting for awhile and I always thought I had this problem too, that it was my ISP blocking port 80. I changed xampp to run on a different port also, and it worked fine then. However, I recently contacted my ISP about it, and they said that they have not blocked it. Any other ideas on what could be? My firewall isn't, and I've portforwarded it correctly. They also said that maybe it was VISTA blocking it because they sometimes block certain things by default such as Remote Assisstance. Any help?