https://grc.com/x/ne.dll?bh0bkyd2
Try there to see if port 80 comes up open. If it is green and not many other ports are (if this is the case then make sure all your comps are firewalled, cause your router isn't protecting you), then your isp probably blocks it. Call 'em to make sure. If you are onc able, check the terms of service. Some cable providers forbid servers of any kind (stupid cable companies...*restrains himself*).
EDIT: almost forgot, if your isp blocks prot 80 but does not forbid servers, some services, like
DynDNS let you redirect a url to another url, so you can actually host off a different port.