You can login to Rank Bullder's membership site here: http://rankbuilder.com/access
Make sure you're using the right username (the email address you purchased the software with) and the password you were either given after purchasing the product or the one you changed it to the first time you logged in.
If you continue to have problems logging in, check to make sure your membership is active. If that doesn't resolve the issue, please open a support ticket and one of our support champs will be happy to help you fix it.