How to Code Log-in form

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C#

SQL

VS2010

Hello Everyone
I'm Creating a Program, for my School project
now I am working at Login form of my Program.

I am getting Exception Error "Object reference not set to an instance of an object"
at

ConfigurationManager.ConnectionStrings["ConnData"].ConnectionString;

using System;
using System.Windows.Forms;
using System.Collections.Generic;
using System.ComponentModel;
using System.Net;
using System.Data.Sql;
using System.Configuration;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Data;
using System.Data.SqlClient;
using System.Text.RegularExpressions;
using System.Runtime.InteropServices;


namespace Proj.Data
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class Login : Window
    {
        public Login()
        {
            InitializeComponent();
            new SplashWindow().ShowDialog();
            
        }
       private void Window_Loaded(object sender, RoutedEventArgs e)
        {
           
        }

        
        private void Exit_Click(object sender, RoutedEventArgs e)
        {
            this.Close();
        }


        private void Button1_Click(object sender, RoutedEventArgs e)
        {
            if ((textBox1.Text != "") && (passwordbox1.Password != ""))
            {
                string connstring = ConfigurationManager.ConnectionStrings["ConnData"].ConnectionString;
                SqlConnection con = new SqlConnection(connstring);
                string q = "select * from Login where UserId = @Username and Password = @Password ";
                SqlCommand cmd = new SqlCommand(q, con);
                cmd.Parameters.AddWithValue("@Username", this.textBox1.Text);
                cmd.Parameters.AddWithValue("@Password", this.passwordbox1.Password);
                con.Open();
                SqlDataReader dr = cmd.ExecuteReader();
                while (dr.Read())
                {
                    if (dr.HasRows == true)
                    {
                        System.Windows.MessageBox.Show("Login Successfully Done");
                    }
                }
                if (dr.HasRows == false)
                {
                    textBlock5.Visibility = System.Windows.Visibility.Visible;
                }
                else
                {
                    textBlock5.Visibility = System.Windows.Visibility.Visible;
                }
            }
        }
       
        private void textBox1_TextChanged(object sender, TextChangedEventArgs e)
        {
            textBlock5.Visibility = System.Windows.Visibility.Hidden;
            if (Keyboard.GetKeyStates(Key.CapsLock) == KeyStates.Toggled)
            {
                textBlock4.Visibility = System.Windows.Visibility.Visible;
            }
            else
            {
                textBlock4.Visibility = System.Windows.Visibility.Hidden;
            }
        }

        private void passwordbox1_PasswordChanged(object sender, RoutedEventArgs e)
        {
            textBlock5.Visibility = System.Windows.Visibility.Hidden;
            if (Keyboard.GetKeyStates(Key.CapsLock) == KeyStates.Toggled)
            {
                textBlock4.Visibility = System.Windows.Visibility.Visible;
            }
            else
            {
                textBlock4.Visibility = System.Windows.Visibility.Hidden;
            }
            
        }

       

       
    }
}

I have a little knowledge about C# and Sql, always looking for Google for Tutorial and it keeps me puzzled.

or Please you can suggest a new Code for my Login