You include jQuery twice (some code removed for brevity):
<!-- load jQuery and sripts -->
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js"></script>
<script type="text/javascript" src="http://engineercreativity.com/samples/obsession/wp-content/themes/EngineerCreativity/js/coin-slider.js"></script>
<link rel="stylesheet" href="http://engineercreativity.com/samples/obsession/wp-content/themes/EngineerCreativity/css/coin-slider-styles.css" />
<script type="text/javascript">
/* SLIDEShOW */
$(document).ready(function() {
$('#coin-slider').coinslider();
});
</script>
<!-- later: -->
<script type='text/javascript' src='http://ajax.googleapis.com/ajax/libs/jquery/1.4.1/jquery.min.js?ver=3.2.1'></script>
Not only is this last URL suspicious (which version did you want, again?!) but this final include overwrites the original jQuery instance (the one with coinslider added!).
Just include jQuery once, and make sure that you do it before you include the coinslider plugin.