While logging in, if you enter in the wrong password three times, you will lock yourself out. Any attempt to log in again will result in an error message indicating the user account in question has been rendered "Inactive."
If your account is on the public server, you will have to contact [email protected] for assistance. If your account is on a private server, contact your administrator instead, who will be able to re-activate your account and send you an email notification with a temporary password.
Upon receipt of the temporary password, you can try logging in again (at which point you will be prompted to provide a new password).
Once the password has been changed successfully, try logging in again.