The map works fine but when I try to add a marker it doesn't work? 

Here is my code so far:

```
<script src="http://maps.googleapis.com/maps/api/js?key=AIzaSyDY0kkJiTPVd2U7aTOAwhc9ySH6oHxOIYM&sensor=false"></script>

<script>
    function initialize()
     {var mapProp = {

center: new google.maps.LatLng(-33.975618,25.585858),
zoom:15,
panControl:true,
zoomControl:true,
mapTypeControl:true,
scaleControl:true,
streetViewControl:true,
overviewMapControl:true,
rotateControl:true,    
mapTypeId: google.maps.MapTypeId.ROADMAP
};
var map = new google.maps.Map(document.getElementById("column2linksmap2"),mapProp);

 var marker = new google.maps.Marker({
  position: latLng,
  title:"Hello World!",
  visible: true
 });
  marker.setMap(map);

 }
  google.maps.event.addDomListener(window, 'load', initialize);

</script>

```