Under what circumstance should I restore the MS SQL Server master database?
You need to restore the master database if you are: a) Rebuilding all your databases from scratch. b) Changing any server-wide or database configuration options. c) Adding logins or other login security-related operations. d) Creating or removing logical backup devices. e) Configuring the server for distributed queries and remote procedure calls such as adding linked servers or remote logins. There is no need to restore your master database, if you just want to restore a user database. For details on Microsoft SQL Server master database, click http://www.microsoft.com/sql/.