Datareader does not return rows

I am trying to build a login screen using a data reader.  For some reason it is not returning rows when in fact there are rows in the database.  I have confirmed this using SQL Server Managerment Studo Express.  Can anyone tell me what I am missing?  

Here is my code:
private String ConnString
    {
        get
        {
            //HDS ConnectionString comes from the Web.Config
            return ConfigurationManager.ConnectionStrings["zxcConnectionString"].ConnectionString;

        }
    }

    protected void btnLogin_Click(object sender, Infragistics.WebUI.WebDataInput.ButtonEventArgs e)
    {
        Boolean valid;
        Boolean npi;
        SqlDataReader reader = null;
        SqlConnection con = null;
        SqlCommand cmd = null;
        String physicianNPI = "";
       

        try
        {
            //Open Connection to the database

            con = new SqlConnection(ConnString);

            // Set up a command with the given query and associate this with the current connection
           
            string CommandText = "SELECT PHYSICIAN_NPI FROM PROVIDER WHERE USERNAME = @username AND PASSWORD = @password";

            cmd = new SqlCommand(CommandText);
            con.Open();
            cmd.Connection = con;

            cmd.Parameters.Add("@username", SqlDbType.VarChar).Value = tbUserName.Text;
            cmd.Parameters.Add("@password", SqlDbType.VarChar).Value = tbPassword.Text;

           

            reader = cmd.ExecuteReader();
            valid = false;
            string test;
            test =reader.GetString(0);
            while (reader.Read())
            {
                valid = true;
                physicianNPI = reader.GetString(0);
            }
            if (valid)
            {
                Session.Add("physicianNPI", physicianNPI);
                Response.Redirect("Portal.aspx");
            }
            else
            {
               lblLoginError.Text = "Invalid Username/Password";
            }
        }
     
       
        finally
        {
            // Close data reader object and database connection
            if (reader != null)
                reader.Close();

            if (con.State == ConnectionState.Open)
                con.Close();
        }
     }Start Free Trial