>>Is the default page a .htm page or dynamic(like .asp)? I would try a simple .htm first. It seems like it's finding your server when you use the IP (based on the message), just not the specific page. Also, double-check the properties in the IIS console, particularly the default pages, etc...
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>It is default.asp and this is listed as one of the defaults. Hmm...

Just some troubleshooting ideas:

Check the IIS logs (you are logging - aren't you?) to see if your server received the request for default.asp. It's possible that some other web server id producing the 404 message (maybe due to a routing issue at your ISP). If default.asp isn't being requested from your server, try a request for default.htm (maybe index.htm too) and see what you get.

If default.asp IS being requested from your server, and it's returning a 404, hmmm, do you have multiple web sites on your server, is the request being picked up by another site on your server?