How to make my ModalPopup image show as Loading/Waiting on asp.net button is clicked?

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C#

ASP.NET

popup

Hi Everyone!

I just want to know how am I going to show a popup loading image(GIF) on button click event. The problem is when I do the this.ModalPopupExtender1.Show(); followed by a line of codes it isn't showing up.

I have this codes:
ASP.NET (ASPX)

<asp:Button ID="btnOK" runat="server" Text="" Style="display:none"
            onclick="btnOK_Click"/>
    <asp:Button ID="btnPopupPanel" runat="server" Text=""
            onclick="btnPopupPanel_Click" />
    <cc1:ModalPopupExtender ID="ModalPopupExtender1" runat="server"
        BackgroundCssClass="modalBackground" PopupControlID="pnlPopupMsg"
        TargetControlID="btnPopupPanel">
      </cc1:ModalPopupExtender>
    <asp:Panel ID="pnlPopupMsg" runat="server" CssClass="modalPopup">
        <table align="center">
          <tr><td align="center"><img src="../../images/ajax_loader_red_512.gif" height="80px" width="80px" /></td></tr>
        </table>
        <div align="center">
            <asp:Label ID="lblLoading" runat="server" Text="Loading..."
            Font-Bold="True" Font-Names="Arial" Font-Underline="False"
            ForeColor="#E52724"></asp:Label></div>
      </asp:Panel>

Situation No.1 :
C# CodeBehind Code

protected void btnSync_Click(object sender, EventArgs e)
       {  this.ModalPopupExtender1.Show();} 

In this situation if its the modalpopupextender is the only code to be executed it shows up but I cannot hide it anymore.

Situation No.2 :
C# CodeBehind Code

protected void btnSync_Click(object sender, EventArgs e)
       {  this.ModalPopupExtender1.Show(); //followed by a line of code/method calls} </pre>

In this situation, the modalpopupextender isn't showing up anymore.

Can somebody explain what wrong with these situations or suggest me more efficient and working popup image? Thanks in advance! Have a nice day everyone!

P.S. I hope my question is clear cause im just new in this organization. ^_^