Microsoft Monitor Class Function Driver Service is a kernel device driver. In Windows 7 it won't be started if the user doesn't start it. If Microsoft Monitor Class Function Driver Service fails to start, Windows 7 attempts to write the failure details into Event Log. Then Windows 7 startup should proceed and the user should be notified that the monitor service is not running because of the error.
The monitor service is using the monitor.sys file that is located in the %WinDir%\system32\DRIVERS folder. If the file is changed, damaged or deleted, you can restore its original version from Windows 7 installation media.