Hi GarryWitt.
The user default database is unavailable at the time of connection. It is possible that the database is in suspect mode or no longer exists. To avoid the error when the user’s default database is unavailable, try to log on as a user who can modify logins. Then, change the user’s default database to a database that is currently available for a connection. If it useless try a special tool - SQL Server Fix Toolbox.
https://www.fixtoolbox.com/sqlserverfix.html
It recovers databases of SQL Server format.
Good luck