Hi @d.o.m.i.n.i.k ,
Try to recover a lost SA password by starting SQL Server in single user mode
Open SQL Server configuration manager and select the service of SQL Server instance. Right-click and click on the Properties option. adding the parameter -m or –f in the startup parameters.
Restart the SQL Server service to start SQL Server in single user mode, Launch the Command Prompt and connect to SQL Server using SQLCMD
create a SQL server login using the below T-SQL script, like:
CREATE LOGIN NewSA WITH PASSWORD = 'Password@1234';
Add the login NewSA to the server level role sysadmin
ALTER SERVER ROLE sysadmin ADD MEMBER NewSA
GO
and then remove the startup parameter -m or -f that is added and restart the SQL Server services
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