Based on the following similar discussion
It depends on where you have the config settings stored. By default IIS7 will have all of it's configuration settings stored in a file called "ApplicationHost.Config". If you have delegation configured then you will see site/app related config settings getting written to web.config file for the site/app. With IIS7 on vista there is an automatica backup file for master configuration is created. This file is called "application.config.backup" and it resides inside "C:\Windows\System32\inetsrv\config" You could rename this file to applicationHost.config and replace it with the applicationHost.config inside the config folder. IIS7 on server release will have better configuration back up story, but for now I recommend using APPCMD to backup/restore your configuration on regualr basis. Example: APPCMD ADD BACK "MYBACKUP" Another option (really the last option) is to uninstall/reinstall IIS along with WPAS (Windows Process activation service).
Also look at this option: How to backup/restore IIS7 configuration
] - Using IIS History
%windir%\system32\inetsrv\appcmd.exe restore backup "My Backup Name"
Details here: Using Configuration History with IIS 7 and IIS 8