Just thought I would add this invaluable bit of SQL as it comes up time and time again here. You only get a couple of attempts to give the correct password to the sa account when loggin into SQL Server before the account becomes locked.
If this happens hopefully you will have a backup admin account or able to log in via integrated authentication.
If this is the case, log in and open a new Query window and type the following:
ALTER LOGIN sa WITH PASSWORD = ‘new_password’ UNLOCK
Job done, the sa account is now unlocked ready for someone to come along and lock it out again!!