It may happen so that you don`t know the password of sa user for SQL Server you inherited from somebody. Actually it can happen cause of many reasons. We`ll try to resolve this issue now.

So here is a step by step guide for resetting forgotten sa password.

1. First of all stop SQL Server service.

2. Run cmd.exe and get to the folder with SQL Server binaries

cd C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\Binn

3. Start SQL Server in single user mode 

sqlservr.exe -m

If you want to run some named instance use the command below:

sqlservr.exe -m -s INSTANCE_NAME

4. Run the following command in cmd.exe:

OSQL -S -E

5. After connecting to the server run the command below:

sp_password NULL, ‘’, ’sa’

GO

6. Stop SQL Server in single user mode by hitting Ctr+C and answering Yes in the dialog.

7. Run SQL Server Service in usual way.

Now you can login under sa with new password.

Please keep in mind that some third-party applications may be using sa password and by changing it you may stop them working, though it is not a good practice to keep sa user enabled and use it by any applications.