Solve “This account is locked.” problem in Magento

If your user has been locked out from the backend, you can reset the lock with one simple query:
UPDATE `admin_user` SET `failures_num` = 0, `first_failure` = NULL, `lock_expires` = NULL WHERE `user_id` = 1;

You can find your user_id with this query:

SELECT `user_id` FROM `admin_user` WHERE `username` = 'admin'