why SqlReader of Read() ts not working

private void swipe_button_Click(object sender, EventArgs e)
        {
            String ID_givenbyUSER = IDtxtBox.Text;                      
            SqlConnection sqlConn = null;
            sqlConn = new SqlConnection("Data Source=HOME-PC\\SQLEXPRESS;Initial Catalog=ABC_SchoolDB;Integrated Security=True");
            sqlConn.Open();
            SqlCommand cmd = new SqlCommand("select Student_Name from dbo.Sheet@Attendance where Serial_Id=" + " ' " + ID_givenbyUSER + " ' ", sqlConn);
            SqlDataReader sqlReader = cmd.ExecuteReader();
            richTxtBox.Clear();
            richTxtBox.AppendText("Hi buddy "); //This line works
            while (sqlReader.Read())
                    {
                        richTxtBox.AppendText("Hi buddy "); //But,Its not work
                        pwdbox.Text =                          (sqlReader["Student_Name"].ToString()); //It also not work
                    }            
            if (sqlConn != null)
            {
                sqlConn.Close();
                sqlConn = null;
            } 
        }
}