In SQL Server Management Studio (SSMS) Object Explorer, right-click the server, and then select Properties. On the Security page, under Server authentication, select ‘SQL and Windows authentication mode’, and then select OK. You have to restart the server.
You can try to access the Database from command line with:
sqlcmd -S server -d database -U username -P password
Example:
sqlcmd -S SQLEXPRESS -d OFFICE_DB -U vs4 -P 123456qAz!
Velislav Krastev Blog 
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