Hello, After looking at your source the reason your drop down menu is not working is when you added the google analytics to your website and did a error in the javascript tags.

Code: 
<script type="text/javascript">
<!--
    // Main vBulletin Javascript Initialization
    vBulletin_init();
//-->

<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
</script>
<script type="text/javascript">
try {
_uacct = "UA-10143129-1";
urchinTracker();
} catch(err) {}</script>


</script>
This is located at the bottom of your footer, change the following code to this:

Code: 
<script type="text/javascript">
<!--
    // Main vBulletin Javascript Initialization
    vBulletin_init();
//-->
</script>

<script src="http://www.google-analytics.com/urchin.js" type="text/javascript"></script>
<script type="text/javascript">
try {
_uacct = "UA-10143129-1";
urchinTracker();
} catch(err) {}</script>
This should fix your issue.

Regards, Dominic