Request a password reset through your account administrator. In most cases, you can regain access to your account by using the self-service page for forgotten passwords. However, if this doesn't help, give us your email address, select an account administrator (if applicable), and send them an email to reset your password. Once they've done this, you'll receive an email with instructions on how to proceed.
If this has jogged your memory, go back to the login page, and login as normal.