Do you get an error message? Have you responded to the email you got when you registered? If you didn't get an email that is the problem, some ISPs block email from AAC without letting you know. If this is the case you probably should open a new email account with Gmail or Yahoo, since they don't close your account after one month of inactivity like Hotmail does. It is always possible you got the email from AAC, but it went into a spam folder and you missed it.
If all else fails you can post in the Feedback and Corrections forum.