Torubleshoot IIS problems

IIS server has six sites configured, suddenly none are reachable. From the server itself, everything works fine; but as soon as I try to reach the sites from outside the network they all return page not found. It is not port forwarding issues, port 80 in the server is reachable. It seems like all requests are being forwarded to the default site instead to the different sites configured on the server (hence giving error 404 page not found). FYI, one of the sites, the most important one, has around six applications configured in different folders; and that is unreachable as well of course. I need someone with enough IIS experience willing to spend one-hour troubleshooting and fixing the problem. I will give you TeamViewer access while I am in front of the server in order to fix the problem. The best money you have ever made!