What is this template? I don't really think that it is from yootheme - all the css is in the head, not in a separate file.
Do you use perhaps a css compression or something? Also the mootools library is not being loaded. you have a plugin most probably that stops it from loading - and you need mootools!
here
<script type="text/javascript" src="/"></script>
<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=true"></script>
<script type="text/javascript" src="http://www.mydive.co/media/com_hotspots/js/more/mootools-1.2.5.1-more.js"></script>
I guess the first script tag should be the mootools.js, but it is not - it is actually nothing. I would advise you to turn most of your plugins off and check if it is working then. Also perhaps change to a different template and see if it is working with it.
Daniel
