1- Click the Windows "Start" button and select "All Programs." Click the "SQL Server" icon. Click "SQL Server Management Studio" to open your console.
2- Right-click the SQL Server database on the left side of the window and select "Tasks." Click "Restore" to open the wizard. Similar to backing up a database, most of the SQL Server defaults are sufficient for quickly recovering a database file.
3- Enter the restoration database name in the "Restore To" text box. This can be the original name of the database, or you can give it a new name.
4- Click the "Add" button in the "Backup Location" section. In the opened dialog window, click your .BAK file and click "OK."
Make sure your paths are the same as the original source of the Database
If there were SDE Geodatabase Locks on the original when the backup was taking place it is likely to cause issues when loaded into the new database.
5- Click "Restore" to recover your database. This may take several minutes, and SQL Server sends a success message when the process is completed.