Web Forms :: Progress Image Is Moving Only One Time When Page Is Loading

I am making one application where i am fetching huge data from database to gridview.

for this it was taking some 30 to 40 seconds. so instead of showing nothing in the page

I am using update panel and update progress bar.

everything is ok but when progress image is showing in the page that time it's moving only one time and stop and before completing page postback.

Here is my code:

 <asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">   
</asp:ToolkitScriptManager>    <div><script language="javascript" type="text/javascript">   
var prm = Sys.WebForms.PageRequestManager.getInstance();  
var popup = $find('<%= modalPopup.ClientID %>');   
prm.add_initializeRequest(InitializeRequest);   

[Code] ....

And here is my code behind:

 protected void Button1_Click(object sender, EventArgs e)    {       
con.Open();       
SqlCommand com = new SqlCommand("select * from processdailydata", con);       
SqlDataAdapter sda = new SqlDataAdapter(com);       
DataSet ds = new DataSet(); sda.Fill(ds);       
GridView1.DataSource = ds;        GridView1.DataBind();        con.Close();    }

i want to show progress image move regularly untile page load is not finished.