Loader not working

in my project i add a loader but it dos't work my code is

<asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1">
<ProgressTemplate>
<div style="position: fixed; text-align: center; height: 100%; width: 100%; top: 0; right: 0; left: 0; z-index: 9999999; background-color: #000000; opacity: 0.7;">
<asp:Image ID="imgUpdateProgress" runat="server" ImageUrl="../assets/ajax-loader.gif"
AlternateText="Loading ..." ToolTip="Loading ..." Style="padding: 10px; position: fixed; top: 45%; left: 50%;" />Loading ...
</div>
</ProgressTemplate>
</asp:UpdateProgress>