SQL: Restore DB Master
It's very very easy...
Run the Rebuild Wizard (Rebuildm.exe), located in the \Program Files\Microsoft SQL Server\80\Tools\BINN directory to rebuild the master database
Start SQL Server in single-user mode by opening up a command prompt and issuing the command sqlservr.exe –c -m from the \Program Files\Microsoft SQL Server\MSSQL\BINN\ directory.
Open Query Analyzer and run the following query:
restore database Master from disk = 'd:\backup\sql\master.bak'