Sql exception unhandled a network related error whilst establishing a network

I am having the above error on con.open() section the error is "Sql exception unhandled a network related error whilst establishing a network" How can I solve this?

public partial class Formlogin : Form
    {
        SqlConnection con = new SqlConnection(@"Data Source=MCFOXXY\AIRAPPS;Initial Catalog=dblogin;User ID=sa;Password=***********");
        public Formlogin()
        {
            InitializeComponent();
        }

        private void buttonLogin_Click(object sender, EventArgs e)
        {
 // bool login = false;

           //SqlConnection con = new SqlConnection(@"Data Source=MCFOXXY\AIRAPPS;Initial Catalog=dblogin;User ID=sa;Password=***********");
            con.Open();
            //string sql = "Select * from  Users where Username='" + textBoxNumber.Text + "' and Password='" + textBoxPassword.Text + "'  ";
            SqlCommand cmd = new SqlCommand("Select * from  Users where Username='" + textBoxNumber.Text + "' and Password='" + textBoxPassword.Text + "'  ");
            SqlDataReader dr = cmd.ExecuteReader();
            dr = cmd.ExecuteReader();
            int count = 0;
           while (dr.Read())
           {
               timer1.Enabled = true;
               count += 1;
           }


           if (count == 1)
           {
               MDIParent1 parent = new MDIParent1();
               parent.Show();
           }
           else
           {
               MessageBox.Show("Error Login");
           }
            dr.Close();
            con.Close();

        }