Networking Help

Hi, I am trying to create a simple remote desktop application but I need some help, Visual C# says "Only one usage of each socket address (protocol/network address/port) is normally permitted" on statement "this.tcpListener.Start();" when I turn the system on more than once. How could I fix that? Here's the code:

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.Net.Sockets;
using System.Threading;
using System.Net;
using System.Runtime.InteropServices;

namespace NickRemoteDesktop
{
public partial class Main : Form
{

[DllImport("user32.dll")]
public static extern void LockWorkStation();

[DllImport("user32.dll")]
public static extern int ExitWindowsEx(int uFlags, int dwReason);

private bool on = false;

private const int password = -2006878815;

private TcpListener tcpListener;
private Thread listenThread;

public Main()
{
InitializeComponent();
Reset();
}

private void Start()
{
this.tcpListener = new TcpListener(IPAddress.Any, 8000);
this.listenThread = new Thread(new ThreadStart(ListenForClient));
this.listenThread.Start();
}

private void ListenForClient()
{
this.tcpListener.Start();
while (true)
{
TcpClient client = this.tcpListener.AcceptTcpClient();
Thread clientThread = new Thread(new ParameterizedThreadStart(HandleClientComm));
clientThread.Start(client);
}
}

private void HandleClientComm(object client)
{
TcpClient tcpClient = (TcpClient)client;
NetworkStream clientStream = tcpClient.GetStream();
byte[] message = new byte[4096];
int bytesRead;
while (true)
{
bytesRead = 0;
try
{
bytesRead = clientStream.Read(message, 0, 4096);
}
catch
{
break;
}
if (bytesRead == 0)
{
break;
}
ASCIIEncoding encoder = new ASCIIEncoding();
switch (encoder.GetString(message, 0, bytesRead))
{
case "-2006878815NLOCK":
LockWorkStation();
break;
case "-2006878815NLOGOUT":
ExitWindowsEx(0, 0);
break;
case "-2006878815NSHUTDOWN":
System.Diagnostics.Process.Start("Shutdown", "-s -t 10");
break;
case "-2006878815NGLOAT":
MessageBox.Show("Nick Rocks!");
break;
case "-2006878815NBLUESCREEN":
Form1 bluescreen = new Form1();
bluescreen.Show();
break;
default:
break;
}
}
tcpClient.Close();
}

private void Stop()
{
this.listenThread = null;
this.tcpListener = null;
}

private void Reset()
{
maskedTextBox1.Text = "";
if (this.on == true)
{
label2.ForeColor = Color.Green;
label2.Text = "ON";
button1.Text = "Turn Off";
Start();
}
else
{
label2.ForeColor = Color.Red;
label2.Text = "OFF";
button1.Text = "Turn On";
Stop();
}
}

private void SubmitKey()
{
if (on == true)
{
if (maskedTextBox1.Text.GetHashCode() == password) this.on = false;
}
else if (on == false)
{
if (maskedTextBox1.Text.GetHashCode() == password) this.on = true;
}
Reset();
}

private void maskedTextBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter) SubmitKey();
}

private void button1_Click(object sender, EventArgs e)
{
SubmitKey();
}

private void button3_Click(object sender, EventArgs e)
{
Application.Exit();
}

private void button2_Click(object sender, EventArgs e)
{
Hide();
}

private void notifyIcon1_DoubleClick(object sender, EventArgs e)
{
Show();
}

}
}

Thanks.