Could not send or receive string through serial cable

//below are both programs that was in computer A and B
// in computer A(the sender)
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading;
using System.IO;
using System.IO.Ports;

namespace MondaySerial
{
    public partial class Form1 : Form
    {
        static SerialPort sp = new SerialPort();
        public Form1()
        {
            InitializeComponent();
        }
        //--------------------------------------------------------------
        private void FormLoad(object sender, EventArgs e)
        {
            sp.PortName = "com1";
            //sp.PortName = "com2";
            sp.BaudRate = 9600;
            sp.DataBits = 8;
            sp.Parity = Parity.None;
            sp.StopBits = StopBits.One;
            sp.Handshake = Handshake.None;
            //
            sp.ReadTimeout = 5000;// Timeout.Infinite;//500;
            sp.Open();
        }
        //-------------------------------------------------------
        protected override void OnClosing(CancelEventArgs e)
        {
            DialogResult result;
            MessageBoxButtons buttons = MessageBoxButtons.YesNo;
            result = MessageBox.Show(this, "Are You Sure Want to exit", " Answer Yes or No",
                buttons, MessageBoxIcon.Question, MessageBoxDefaultButton.Button1,
                MessageBoxOptions.RightAlign);
            if (result == DialogResult.Yes)
            {
                sp.Close();
                //-------------------
                //ButtonForm1.ActiveForm.Close();
                //this.Close();
                Application.Exit();
            }//Yes
            else e.Cancel = true;
        }
        //---------------------------------------------------------
        private void SendStringClick(object sender, EventArgs e)
        {
            sp.WriteLine(textBox2.Text);
        }
        //----------------------------------------------------------
    }
}

// and in computer B (the receiver )

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

namespace MondaySerial
{
    public partial class Form1 : Form
    {
        static SerialPort sp = new SerialPort();
        public Form1()
        {
            InitializeComponent();
        }
        //--------------------------------------------------------------
        private void FormLoad(object sender, EventArgs e)
        {
            sp.PortName = "com1";
            //sp.PortName = "com2";
            sp.BaudRate = 9600;
            sp.DataBits = 8;
            sp.Parity = Parity.None;
            sp.StopBits = StopBits.One;
            sp.Handshake = Handshake.None;
            //
            sp.ReadTimeout = 5000;// Timeout.Infinite;//500;
            sp.Open();
        }
        //-------------------------------------------------------
        protected override void OnClosing(CancelEventArgs e)
        {
            DialogResult result;
            MessageBoxButtons buttons = MessageBoxButtons.YesNo;
            result = MessageBox.Show(this, "Are You Sure Want to exit", " Answer Yes or No",
                buttons, MessageBoxIcon.Question, MessageBoxDefaultButton.Button1,
                MessageBoxOptions.RightAlign);
            if (result == DialogResult.Yes)
            {
                sp.Close();
                //-------------------
                //ButtonForm1.ActiveForm.Close();
                //this.Close();
                Application.Exit();
            }//Yes
            else e.Cancel = true;
        }
        //---------------------------------------------------------
        private void ReadStringClick(object sender, EventArgs e)
        {
			textBox2.Text =  sp.ReadLine();
        }
        //----------------------------------------------------------
    }
}