How to hide the page on load indicating in asp.net - asp.net

Question

I am using ASP.NET 2.0 and AJAX extension tool.
I already created loading indicator on button submit. When I will click the button, the loading indicator will show after redirecting to the next page. But, I want to hide the page until processing has completed (after that redirect to next page).
I am using the following code:
<td style="width: 100px; height: 26px;">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdateProgress ID="UpdateProgress1" DynamicLayout="false" runat="server">
<ProgressTemplate>
<img src="Images/loading.gif" alt="Images/loading.gif" style="z-index: 100; left: 21px; position: absolute; top: 64px" />
</ProgressTemplate>
</asp:UpdateProgress>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<dx:ASPxButton ID="btnOk" ClientInstanceName="btnok" runat="server" Style="z-index: 100; left: 90px; position: absolute;
top: 108px" Text="OK" Width="61px" BackColor="Gainsboro" OnClick="btnOk_Click" AutoPostBack="False" >
<DisabledStyle>
<Border BorderColor="Teal" />
</DisabledStyle>
<ClientSideEvents Click="function(s, e) {
ShowloadingImage();
}" />
</dx:ASPxButton>
</ContentTemplate>
</asp:UpdatePanel>

Answer 1

To "hide" your page you can make an overlay div over all, using this css
.OverAll
{
height:100%;
width:100%;
position:fixed;
left:0;
top:0;
z-index:2 !important;
background-color:black;
}

Answer 2

using jquery we can hide the page on page loading...I am using following code
$(function() {
($.unblockUI);
$('#pnlLogin_btnOk').click(function() {
$.blockUI({ message: '<img src="Images/loading.gif" />' });
});
});