c# webbroswer not working properly

Hi everyone!

I'm a beginner developer so I have to ask for some help!

I've written this :

WebBrowser personal = new WebBrowser();
            personal.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(refresh);
            personal.Url = new Uri("http://localhost/linko.php");
            Application.EnableVisualStyles();
        }
        private static void refresh(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            WebBrowser personal = (WebBrowser)sender;
            HtmlDocument page = personal.Document;
            HtmlElement username = page.GetElementById("username");
            username.SetAttribute("username", "bobidi");
            HtmlElement pass = page.GetElementById("password");
            username.SetAttribute("password", "babidi");
            HtmlElement submitButton = page.GetElementById("Gianni");
            submitButton.InvokeMember("click");

        }

and it was suppose to browse a web page(in localhost that I made to test my code)....The problem is that it run but it doesn't work cuz in debugging mode I noticed that Url attribute associated to WebBroswer is NULL!!!! Can anyone help me??!!!

Thanks you very much!