Cannot recover the master database. SQL Server is unable to run. Restore master from a full backup, repair it, or rebuild it. For more information about how to rebuild the master database, see SQL Server Books Online.

We had windows server maintenance this weekend after reboot the server SQL Server could not start. What i noticed that windows update installation had failed. In the event viewer i have found that Cannot recover the master database. SQL Server is unable to run. Restore master from a full backup, repair it, or rebuild it. For more information about how to rebuild the master database, see SQL Server Books Online. Script level upgrade for database 'master' failed because upgrade step '[login to view URL]' encountered error 2627, state 1, severity 14. This is a serious error condition which might interfere with regular operation and the database will be taken offline. If the error happened during upgrade of the 'master' database, it will prevent the entire SQL Server instance from starting. Examine the previous errorlog entries for errors, take the appropriate corrective actions and re-start the database so that the script upgrade steps run to completion. I never did this before. i am litterally scared of doing this. in the production environment. Databases are not many only 5/6. Please help.