How to bring your SQL database online

• Open Management Studio and in the "Connect to Server" dialog box enter your connection parameters
• Click the "Options >>" button and navigate to the "Connections Properties" page
• In the "Connect to database" dialog box type the word master.
• Open up a New Query window and paste the following T-SQL code into it:

USE [master] 
click on GO  

Then

ALTER DATABASE [DB_123_database] SET ONLINE 
Click on GO

• Execute the code
• If the code executed successfully, but you do not see the change in your database status, disconnect from the server and connect again. This time, you can connect to your default database instead of master.