Your Twitter account might be locked in for 2 reasons. It may be briefly locked in in the event that you have exceeded the permitted amount of failed login attempts. Your account is mechanically locked for just one hour, in case it was locked because of this reason. Another motive your account might be locked is in the event you set your account to "Shielded." Your tweets cannot be re-tweeted and those who would like to follow you must be manually approved by you. It's possible for you to establish your account in your account settings again to Public.