C#:only the backgroundwork running

[touyara]

Hi every one!
I am trying to create a port scanner , I would be able to generate numbers of backgroundworker and each bgwork would scan ports simultaneously, but when I generate 10 bgworkers, there is only the last one working ?! I don't know why? but if I re-click the button there is another bgworker come out and working simultaneously, any body know the reason ? please full fill my knowledge!
thank you

       private void DoAsSyncScan(int index,int begin = IPEndPoint.MinPort, int end = IPEndPoint.MaxPort)
        {
            String ScanAddress;
            IPAddress ScanIPAddress;
            startedflg = true;
            try
            {
                ScanAddress = "127.0.0.1";
                Action atxtb = () =>
                {
                    if (textBoxIP.Text != string.Empty)
                        ScanAddress = textBoxIP.Text;
                };
                Dispatcher.BeginInvoke(atxtb);

                // Both a hostname or an IP address are fine
                if (PortScanning.PortScanning.IsIpAddress(ScanAddress))
                {
                    ScanIPAddress = IPAddress.Parse(ScanAddress);
                }
                else if (!PortScanning.PortScanning.LookupDNSName(ScanAddress, out ScanIPAddress))
                {
                    MessageBox.Show("Error looking up {0}", ScanAddress);
                    return;
                }

                // Report what we are going to do

                // Scan all the possible posts
                for (int Port = begin; Port < end; Port++)
                {
                    //invoke the dispatcher and pass the percentage and max record count
                    Action act1 = () =>
                    {
                        this.UpdateProgressText(index, (begin - begin / end - begin) * 100, end - begin, Port);
                    };
                    Dispatcher.BeginInvoke(act1);
                    var r = dt.NewRow();
                    if (PortScanning.PortScanning.ScanPort(ScanIPAddress, Port))
                    {
                        r["Port"] = Port + "";
                        r["Status"] = "Opened";
                        Action act2 = () =>
                        {
                            dt.Rows.Add(r);
                        };
                        //Parallel.Invoke(act2);
                        Dispatcher.BeginInvoke(act2);
                    }
                    System.Threading.Thread.Sleep(10);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
        BackgroundWorker[] bgworkers;
        System.Data.DataTable dt = new System.Data.DataTable();
        private void buttonScan_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                bgworkers = new BackgroundWorker[(int)this.decimalUpDownThread.Value];
                int part = (int)Math.Ceiling((double)IPEndPoint.MaxPort / (double)this.decimalUpDownThread.Value);
                int begin = 0;
                Action act0 = () =>
                    {
                        this.dataGrid1.DataContext = dt.DefaultView;
                    };
                
                Dispatcher.BeginInvoke(act0);
                for (; begin < bgworkers.Length; begin++)
                {
                    bgworkers[begin] = new BackgroundWorker();
                    bgworkers[begin].WorkerSupportsCancellation = true;
                    DoJobs( bgworkers[begin], begin, part);                    
                }
                foreach (var item in bgworkers)
                {
                    item.RunWorkerAsync();  
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
                     
        }
        public void DoJobs(BackgroundWorker bgx,int begin,int part)
        {
            bgx.DoWork += (wsender, we) =>
            {
                System.Console.WriteLine("started:{0}",we.Argument);
                if (IPEndPoint.MaxPort > (begin + 1) * part)
                    DoAsSyncScan(begin, begin * part, begin * part);
                else
                    DoAsSyncScan(begin, begin * part, IPEndPoint.MaxPort);  
            };     
            //System.Threading.Thread.Sleep(1000);                       
        }