The vast majority of home users get their IP address dynamically. This means it changes periodically, so the chances are that your issue is related to a cached web site cookie rather than an IP address.
I suggest you clear out your cookie cache (Or if you know enough about the browser you are using, look for and delete any cookies related only to this web site.) I bet that'll fix your issue.
A quick test would be to try and access this web site using your browser's "Private" mode from the computer having the issue. (Chrome calls it "Incognito; Firefox calls it "Private"; So does Safari) If it works then, cookies are definitely the culprit.
Cheers,
Dan K.