HttpCookie cok = new HttpCookie("SampleCookie");
            cok.Expires.AddDays(1);
            cok.Values.Add("Username", txtUsername.Text);
            cok.Values.Add("Password", txtPassword.Text);
            Response.Cookies.Add(cok);

   if (!Page.IsPostBack)
            {
                HttpCookie cookie = Request.Cookies["SampleCookie"];
                if (cookie != null)
                {
                    txtUsername.Text = cookie.Values["Username"];
                    //txtPassword.Text = cookie.Values["password"];  //This wont display the password in the password textbox
                    txtPassword.Attributes.Add("Value", cookie.Values["password"]); //This will work

                }
            }