Setting database option SINGLE_USER to ON for database

You can find more details on following post

http://support.microsoft.com/kb/911847
http://support.microsoft.com/kb/259551
http://support.microsoft.com/kb/247181/EN-US/
http://support.microsoft.com/kb/274799/

Login failed for user 'sa'. [CLIENT: ]

You can find more details on following post

http://support.microsoft.com/kb/322336
http://blogs.msdn.com/sql_protocols/archive/2006/02/21/536201.aspx
http://www.eggheadcafe.com/forumarchives/SQLServersecurity/Jul2005/post23406881.asp
http://social.msdn.microsoft.com/forums/en-US/sqldataaccess/thread/a50f79ab-a877-4e50-a5bc-8bd0f88384a2/
http://www.tek-tips.com/viewthread.cfm?qid=1344607&page=11
http://support.microsoft.com/kb/907284

How to: Change Server Authentication Mode

You can find more information on MSDN
http://msdn.microsoft.com/en-us/library/ms188670.aspx