After going through this pain ourselves we've found the most straightforward way to unlock an account is to run this TSQL as sysadmin:
ALTER LOGIN TestLogin WITH PASSWORD = 'Test^123' UNLOCK
This changes the password and unlocks the account. Unchecking the "Login is locked out" box in SSMS is useless.
As for the OP, he'll have to find another admin login to use so he can unlock the account. If the Dedicated Administrator Connection is configured, the OP could use that to connect to the instance and unlock the login. See "Dedicated Administrator Connection" in BOL.