Sql server 2008 R2 Forget Password for Sa

1. Open the command prompt (Right-Click on and select "Run As Administrator")
2. From the command prompt type net stop MSSQLSERVER
3. Next type net start MSSQLSERVER /m
4. Open SQL Server Management Studio. Do not login, cancel the login dialog.
5. From the file Menu select New->Database engine query, and login (Make sure you use the host name and not localhost).
6. Execute the query ALTER LOGIN sa WITH PASSWORD = ''; to reset the password (if the sa is not enabled then type ALTER LOGIN sa ENABLE to do so)
7. Login with the sa user and add the Administrator user.