Password Protect Pages in ASP.Net

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ASP.NET4

Hello friends
My name is Sarfaraz. I am facing a problem in securing few pages of my asp.net website where I am supposed to secure few pages from all users other than ad admin only a single person with a username and password stored in SQL server. Everything is working fine but when i type the url of the secured page directly in the address bar it gets opened up without redirecting to the login page first.Please help
my code is

<br />
 private bool AuthenticateUser(String username, string password)<br />
    {<br />
        string cs = ConfigurationManager.ConnectionStrings["HamdardConnectionString"].ConnectionString;<br />
        using (SqlConnection con = new SqlConnection(cs))<br />
        {<br />
            SqlCommand cmd = new SqlCommand("mp_authenticateadmin",con);<br />
            cmd.CommandType = CommandType.StoredProcedure;<br />
<br />
            SqlParameter paramUsername = new SqlParameter("@Username",username);<br />
            SqlParameter paramPassword = new SqlParameter("@Password", password);<br />
<br />
            cmd.Parameters.Add(paramUsername);<br />
            cmd.Parameters.Add(paramPassword);<br />
<br />
            con.Open();<br />
            int ReturnCode = (int)cmd.ExecuteScalar();<br />
            return ReturnCode == 1;<br />
<br />
<br />
        }<br />
<br />
    }<br />
  <br />
 <br />
    <br />
    protected void btnloginn_click(object sender, EventArgs e)<br />
    {<br />
        if (AuthenticateUser(txtusername.Text, txtpassword.Text))<br />
        {<br />
            FormsAuthentication.RedirectFromLoginPage(txtusername.Text,true);<br />
<br />
<br />
        }<br />
        else<br />
        {<br />
            lblerror.Text = "Invalid Username or /and Password";<br />
<br />
        }<br />
    }<br />
<br />

and my web.config file is

<br />
<configuration><br />
  <connectionStrings><br />
    <add name="HamdardConnectionString" connectionString="Data Source=localhost;Initial Catalog=Hamdard;Integrated Security=True"<br />
      providerName="System.Data.SqlClient" /><br />
  </connectionStrings><br />
    <br />
  <system.web><br />
    <compilation debug="true" targetFramework="4.0"/><br />
<br />
      <authentication mode="Forms"><br />
          <forms loginUrl="Login.aspx" defaultUrl="Default.aspx"><br />
          </forms><br />
      </authentication><br />
<br />
<br />
      <authorization><br />
          <deny users ="?" /><br />
          <br />
      </authorization><br />
    </system.web><br />
</configuration><br />