On this website:

Under the phone number in the header there is a little blue arrow that slides down the slider, which works perfectly. However, clicking the arrow again should slide the slider backup but nothing is happening.

Here is the jQuery handling this:
$('#open-slider').click(function() {		
	if($("#slider").is(":hidden")) {
		$(this).animate({"background-position": "17px 0"});
		$("#slider").animate({"margin-top": "-490px"});
		$('header').animate({"margin-bottom": "45px"});	
	} else {
		$(this).animate({"background-position": "0 0"});
		$("#slider").animate({"margin-top": "0"});
		$('header').animate({"margin-bottom": "490px"});

Any help would be greatly appreciated.