Is Apache installed? Is xinetd watching port 80?
Is there anything in the log about not being able to bind port 80?
Ok, here's how I would track this down. I'd get the permission to do this from all the admins involved, though, as what I'm going to describe will be detected by most IDS's as an intrusion attempt.
I would runt a standard traceroute to see what hosts lie on the path from you to the server in question. Then, I'd run an nmap idlescan ( see http://www.insecure.org/nmap/idlescan.html ) using each host on the path as the zombie along the way. This can allow you to find where port 80 is being blocked.
