>>I knew this would happen; that some day I will mess up my test SQL database and will need to replace it with the backup. Fortunately, I do make routine backups. What I have is the .bak version of the DB. For example, MyTestDatabase.bak; which is on the external drive. And I have the actual database, MyTestDatabase in the SQL Server 2008.
>>What steps should I take to replace the damaged one with the .bak from the external drive?
>>
>>TIA
>
>I created a database, named it 'test'.
>Then I selected this database -> Tasks -> Restore database.
>Selected From Device and located the MyDatabase.bak (on the external drive).
>Checked the box Restore.
>Then error message:
>

>The backup set holds a backup of a database other than the existing 'test' database
>

>
>What am I doing wrong?

You need to go into the "Files" tab and make sure to move the physical MDB files into the path of the new database. This is usually for the database and the logs two separate files, both which need to be redirected to the new location.