How I Can Do Pop Up Window In .Asp

You can achieve this simply using javascript libraries, for example most popular is jQuery UI. Look at the following:

http://jsfiddle.net/robschmuecker/9z2ag/1/[^]

http://salman-w.googlecode.com/svn/trunk/jquery-ui-dialog/modal-dialog-with-buttons.html[^]

More examples:
http://salman-w.blogspot.fr/2013/05/jquery-ui-dialog-examples.html[^]

https://www.safaribooksonline.com/library/view/jquery-ui/9781449325176/ch04s05.html[^]

you can also try ExtJS library, but it's heavier than jQuery and must be used for binding data grids and creating extended web UI.

http://docs.sencha.com/extjs/4.0.7/extjs-build/examples/message-box/msg-box.html[^]

The could should look like this:

<div id="dialog" title="Dialog">
        <p>This dialog was created on document ready event with <code>autoOpen</code> set to <code>false</code>.</p>
        <p>It was opened by calling <code>.dialog(&quot;open&quot;)</code> method.</p>
    </div>
    <input type="button" id="button" value="Click to open the dialog">

javascript, that shows popup:

<script>
        /*
         * jQuery UI Dialog: Open Dialog on Click
         * http://salman-w.blogspot.com/2013/05/jquery-ui-dialog-examples.html
         */
        $(function() {
            $("#dialog").dialog({
                autoOpen: false
            });
            $("#button").on("click", function() {
                $("#dialog").dialog("open");
            });
        });
    </script>