How to solve this : Unable Open Browse Button after running the windows application

string n;
      byte[] b1;
      OpenFileDialog op;


      private void btnBrowse_Click(object sender, EventArgs e)
      {
            op = new OpenFileDialog();
          if (op.ShowDialog() == DialogResult.OK)
          {
              string t = textBox1.Text;
              t = op.FileName;
              FileInfo fi = new FileInfo(textBox1.Text = op.FileName);
              n = fi.Name + "." + fi.Length;
              TcpClient client = new TcpClient("DELL", 5055);
              StreamWriter sw = new StreamWriter(client.GetStream());
              sw.WriteLine(n);
              sw.Flush();
              label1.Text = "File Transferred....";
          }





      }

      private void btnSend_Click(object sender, EventArgs e)
      {
          TcpClient client = new TcpClient("DELL", 5050);
          Stream s = client.GetStream();
          b1 = File.ReadAllBytes(op.FileName);
          s.Write(b1, 0, b1.Length);
          client.Close();
          label1.Text = "File Transferred....";
      }