Openfiledialog() problem with oledbconnection() not clearing

<pre lang="C#">OpenFileDialog openFileDialog1 = new OpenFileDialog();
    openFileDialog1.FileName = String.Empty;
    openFileDialog1.Filter = "All files (*.*)|*.*";
    openFileDialog1.Title = "Select Your - Excel File :- ";
    if (openFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK) {
            String MyExcelFile = openFileDialog1.FileName;

            //Below For XLSX Format
        String StrConn2 = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + MyExcelFile + "; Extended Properties=\"Excel 12.0; HDR=YES; \"";

            String MyExcelSheet = "[Sheet1$]";
            String MySQLSelect = "select * from " + MyExcelSheet;
            System.Data.OleDb.OleDbConnection Cn1 = new System.Data.OleDb.OleDbConnection(StrConn2);
            System.Data.OleDb.OleDbDataAdapter Da1 = new System.Data.OleDb.OleDbDataAdapter(MySQLSelect, Cn1);
            Cn1.Open();
            Da1.Fill(MyContactsTbl);
            Cn1.Close();
            Cn1.ReleaseObjectPool();
            Cn1 = null;
            MessageBox.Show(MyExcelFile);


        }