how to show this loading image when second time a button is clicked?

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ASP.NET

Javascript

Ajax

jQuery

function PerformCalculationWithImageProgress()
{
        $("imgProgress").show();
        $.get("Default.aspx", function(data, textStatus)
        {
                $("imgProgress").hide();
                alert(data);
        });
}

<input type="button" name="btnDoRequest" value="Perform calculation" onclick="PerformCalculationWithImageProgress();" />
<img src="loading.gif" style="display: none;" id="imgProgress" alt="" />

the above code works only for first time button click and then it hides the loading bar..but i want it to show even if i click multiple time...