Ah, that's probably because of failed login attempts. It should be reset after some time and you'll be able to login.
If you're in a hurry, you can login to your FTP and rename the s2Member directory to deactivate it and the protection won't be there anymore.
/wp-content/plugins/s2member/You can edit the setting for this restriction under:
WP Admin -> s2Member -> Restriction Options -> Brute Force IP/Login Restrictions.
I hope that helps.
