Visual studio 2010 C# Serial, can`t read port.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO.Ports;


namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            getAvailablePorts();     
        }
        void getAvailablePorts()
        {
            string[] ports = SerialPort.GetPortNames();
            comboBox1.Items.AddRange(ports);
        }
        private void button2_Click(object sender, EventArgs e)
        {
            try
            {
                if(comboBox1.Text==""){
                    readBox.Text = "Select Port COM";
                }
                else
                {
                    serialPort1.PortName = comboBox1.Text;
                    serialPort1.BaudRate = 115200;
                    serialPort1.Parity = Parity.None;
                    serialPort1.StopBits = StopBits.One;
                    serialPort1.Handshake = Handshake.None;
                    serialPort1.Open();
                    initButton.Enabled = false;

                    sendButton.Enabled = true;
                    readButton.Enabled = true;
                    disconnectButton.Enabled = true;
                    //
                    serialPort1.DataReceived += new SerialDataReceivedEventHandler(serialPort1_DataReceived);
                }
            }
            catch (UnauthorizedAccessException)
            {
                readBox.Text = "Error";
            }
        }

        private void richTextBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            comboBox1.Text = serialPort1.PortName;    
        }

        private void sendButton_Click(object sender, EventArgs e)
        {
            serialPort1.WriteLine(input1.Text);
            input1.Text = "";         
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private string DispString; 
        
        private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            DispString = serialPort1.ReadExisting();
            this.Invoke(new EventHandler(DisplayText));
            
        }
        //
        private void DisplayText(object sender, EventArgs e)
        {
            readBox.AppendText(DispString);    
        }


        private void readButton_Click_1(object sender, EventArgs e)
        {
            try
            {
                //readBox.Text = serialPort1.ReadExisting();
                 
            }
            catch (TimeoutException)
            {
                readBox.Text = "timeout";
            }
        }

        private void disconnectBotton_Click(object sender, EventArgs e)
        {
            initButton.Enabled = true;
            sendButton.Enabled = false;
            readButton.Enabled = false;
        }

        private void readBox_TextChanged(object sender, EventArgs e)
        {

        }
    }
}