For checking whether Google public dns is working or not, after saving the settings mentioned above do the following procedure. Enter a site address in your browser, for eg. www.google.com and check whether the Google homepage is loading or not. If it’s loading, then bookmark this page and try acessing google from bookmark. If that works, the Google public DNS is configured successfully on your system.
If Google homepage doesn’t load, then enter an ip address like http://184.108.40.206/ and check whether it goes to the website http://eecs.mit.edu. If that page loads then you are having problems configuring Google Public DNS. Roll back the changes and check for any website, if it still doesn’t load check your internet connection.