C# Form не прогружается

Форма WaitingDialogcs не прогружается, но когда метод GetPage законьчил работу загрузалиась

Form3
 private void LoadingCams()
    {
        startRange = Convert.ToInt32(textBox1.Text);
        endRange = Convert.ToInt32(textBox2.Text);
        WaitingDialogcs WD = new WaitingDialogcs();
        WD.Visible = true;
        WD.GetPage();
        foreach (string gg in aa)
        {
            if (gg != null)
                listBox1.Items.Add(gg);
        }
    }
WaitingDialogcs
public WaitingDialogcs()
    {
        InitializeComponent();
    }
    public void GetPage()
    {
        string[] cams = new string[Form3.endRange - Form3.startRange];
        int a = 0;
        string url;
        for (int i = Form3.startRange; i <= Form3.endRange; i++)
        {
            try
            {
                url = "https://geocam.tv/streamer/" + i + ".mjpg";
                HttpWebRequest myHttpWebRequest = (HttpWebRequest)WebRequest.Create(url);
                HttpWebResponse myHttpWebResponse = (HttpWebResponse)myHttpWebRequest.GetResponse();
                if (myHttpWebResponse.StatusCode == HttpStatusCode.OK)
                {
                    myHttpWebResponse.Close();
                    cams[a] = url;
                    a++;
                }
                Class1.reply = "Response Status Code is OK and StatusDescription is:" + myHttpWebResponse.StatusDescription;
            }
            catch (WebException e)
            {
                Class1.reply = "WebException Raised. The following error occured : " + e.Status;
            }
            catch (Exception e)
            {
                Class1.reply = "The following Exception was raised : " + e.Message;
            }
            Class1.S_int = i;
            Class1.E_int = Form3.endRange;

            label1.Text = "Cheking Cams . . . .";
            label2.Text = "[" + Class1.S_int + "/" + Class1.E_int + "]";
            listBox1.Items.Add(Class1.reply);
            listBox1.SelectedIndex = listBox1.Items.Count - 1;
            listBox1.SelectedIndex = -1;

        }
        for (int i = 0; i < Form3.endRange; i++)
        {
            Form3.aa[i] = cams[i];
        }
    }