pls flow below step:
1.Rebuild the master database. In SQL Server 6.5, you will have to run setup in the SQL Server program file group. In 7.0 run Rebuildm.exe in the \Mssql7\Binn directory.
2.Place SQL Server in single user mode. This can be done by starting SQL Server with the -m parameter.
3.Restore your master database from the last known good backup.
Verify that the master database was successful restored.
Confirm that all the databases are up an running.
4.Restore the MSDB database from the last known good backup.
5.Stop and start SQL Server in normal mode.
6.Open your database for production users.
the other way in SQL Server 7.0 or 2000 you can use sp_attach_db