Exposing IIS to the outside world without a heavy-duty firewall in place is simply *asking* to have your system broken into.
"Maybe", "probably", even.
Did you try:
1) reading your service agreement to see what it says about running servers? 2) *asking* the SBC support people if you are allowed to run servers? 3) asking the SBC support people if they block incoming port 80 requests.
Comment: If you don't have the knowledge/skills to investigate/troubleshoot a matter like this yourself, you should _not_ be attempting to set up an "exposed to the world" server on the Internet, by yourself. Get somebody who _knows_ _what_they_are_doing_ to go over *everything* on that box (and the rest of your local network), and who can recommend/specify a good hardware-based firewall -- *and* who can diagnose _why_ contact from the outside world "doesn't work".