If a user has five consecutive invalid login attempts, the user's account is locked. An email is automatically sent to the user. You can manually reset the account or wait until the account is automatically reset, which is 60 minutes after the 5th failed attempt.
On the Manage User page, the Login Failures field displays the number of unsuccessful login attempts for that user's account. By resetting this counter, you unlock the account. If the Login Failures field is less than 5, the user's account is not locked but you can still reset the counter to 0.
To reset the counter, click the Reset Login Failures Count link on the right side of the page under Tasks.