By mistake I changed my multiuser SQL Server database to single user. I can not return the value to multiuser since I do not have permissions. Can you help me with the password of the SA user or return the value, this is the error:
Cannot open user default database. Login failed. Login failed for user 'S192-169-158-19\gpoinnovador'. (.Net SqlClient Data Provider)
Thanks for posting. I'm not sure you still need help with this, but if you're using a control panel, like Plesk, and need the password for your SQL Server's "sa" user, you can usually reset the password via that control panel. However, the database server must have already been added to Plesk, Plesk must be able to connect to SQL Server already, and it must have been initially connected using the sa user.
Otherwise, you'll typically need to restart SQL Server in single-user mode. This should be possible via RDP and the SQL Server Configuration Manager. Then, you should be able to access SQL Server through a program similar to SQL Server Management Studio in order to change the password for the sa user. Once you have reset the password for the sa user and have ensured that user is allowed to connect you'll want to revert SQL Server to multi-user mode.