<asp:LinkButton ID="asp_order_open" runat="server" class="a_menu"  PostBackUrl="" Visible="True"><div>Сделать заявку</div></asp:LinkButton>

    Protected Sub asp_order_open_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles asp_order_open.Click
        asp_order.Visible = True
    End Sub

<asp:Panel ID="asp_order" runat="server"  Visible="false">
     
     <div id="TB_overlay"></div>     
         <div style="padding: 20px; background-color: #CCCCCC; z-index: 7000;   position: fixed; margin:auto;" >
         <asp:Label ID="Label1" runat="server" Text=" NameProduct_variable " Visible="False">  </asp:Label>    
         <asp:ImageButton ID="asp_order_close" runat="server" Visible="true" style="position: absolute; top: -15px; right: -15px"  ImageUrl="/App_Themes/Images/Default/close.png" PostBackUrl="#" />
         <div class="message_left_div">
             <asp:Image ID="Image_Orders" runat="server" /></div>
         <div class="message_left_div">   
            <div class="message_head">Отправить заявку, приложив данное фото в качестве примера </div>
            <div><input ID="myname"  runat="server" type="text" placeholder="Имя Фамилия *" class="message_body" /></div>
            <div><input ID="email"  runat="server" type="text" placeholder="E-mail: *" class="message_body" /></div>
            <div><input ID="phone"  runat="server" type="text" data-mask="+7 (999) 999-99-99" placeholder="Телефон *" class="message_body" /></div>
            <div><input ID="company"  runat="server" type="text" placeholder="Компания (необязательно)" class="message_body" /></div>
            <div><input ID="comment"  runat="server" type="text" placeholder="Ваш комментарий (необязательно) " class="message_body" style="height: 90px" /></div>
            <asp:Button ID="Button_send_mail" Text="Отправить сообщение"  runat="server" Width="300" Height="25" PostBackUrl="#" />
 

          
            <div class="message_head"><asp:Label ID="message_site" runat="server" Visible="false" Text="Сообщение отправлено." /></div>
          </div> 
          </div>
 
  </asp:Panel>

<asp:LinkButton ID="asp_order_open" runat="server" class="a_menu"  PostBackUrl="" Visible="True"><div>Сделать заявку</div></asp:LinkButton>
<asp:Label ID="Label_asp_order_open" runat="server" Text="Label"></asp:Label>

    Protected Sub asp_order_open_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles asp_order_open.Click
asp_order.Visible = True
Label_asp_order_open.Text="Вы нажали кнопку"
    End Sub