I know its probably something simple, but for the life of me I cannot figure out why my navigation drop-down stopped working.

HTML
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
	<head>
		<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
		<link rel="stylesheet" type="text/css" href="lib/style.css" />	
	</head>

	<body>
		<div id="wrapper">
			<div id="header">
				<ul id="nav">
					<li><a href="index.php">Home</a>
						<ul>
							<li><a target="new" href="/Forums">Forums</a></li>
						</ul>
					</li>

					<li><a href="Contacts.php">Contacts</a>
						<ul>
							<li><a href="contacts_admin.php">Admin</a></li>
						</ul>
					</li>
				</ul>
                        </div>
		
			<div id="content">
				<div id="sidebar"> Sidebar </div>

				<div id="main">
					MAIN
				</div>
			</div>
		
			<div id="footer"> FOOTER </div>
		</div>
	</body>
</html>

CSS
Code:
html,
body
{
	background: #909EAB url(images/bg.png);
	height: 100%;
	margin: 0;
	padding: 0;
}

#wrapper
{
	height:100%/9;	/* For IE8 and below */
	min-height: 100%;
	position: relative;	
}

#header
{
	background: #EFEFEF;
	width: 100%;
}

#content
{
	padding-bottom: 60px; /* Height of the footer element */
}

#sidebar
{
	background: pink;
	float: left;
	padding: 10px;
	width: 20%;
}

#main
{
	background: tan;
	padding-top: 30px;
}

td
{
	border: 1px solid black;
	color: black;
	font-size: 0.80em;
}

/*---------------------------------*/
/*---------- Navigation ----------*/
/*-------------------------------*/


/*----- ALL LISTS -----*/
#nav, 
#nav ul 
{
	background: #EFEFEF;
	float: left;
	margin: 0;
	padding-bottom: 1px;
	padding-left: 5px;
	width: 99.5%;
	z-index:9999;
}

#nav li
{
	display: inline;
	float: left;
	font-family: "Book Antiqua", Georgia, serif;
	font-size: 90%;
	font-weight: bold;
	list-style: none;
	margin-right: 50px;
	text-align: left;
}

#nav a
{
	color: #757575;
	text-decoration: none;
}

#nav a:hover
{
	background-color: #5F6975;
	color: #FFFFFF;
}



/* ----- SECOND LEVEL LISTS -----*/
#nav li ul
{
	background: #5F6975;
	left: -999em;
	position: absolute;
	width: 150px;
}

#nav li ul li
{
	width: 155px;	
}


#nav li ul a
{
	color: #FFFFFF;
	font-size: 1em;
	padding-bottom: 5px;
	padding-left: 5px;
	padding-right: 5px;
	padding-top: 5px;
}


#nav li ul a:hover, a.sfhover
{
	background-color: #4b545f;
	color: #FFFFFF;
}



/*---------------------*/
/* ----- FOOTER ------*/
/*-------------------*/

#footer
{
	bottom: 0;
	border-top: 2px solid grey;
	height: 60px;
	left: 0;
	position: absolute;
	width: 100%;
}

#footer cite
{
	display: block;
	font-size: 0.65em;
	font-style: normal;
	font-weight: bold;
	letter-spacing: 1px;
	margin-right: 25px;
	text-align: right;
	text-transform: uppercase;
}

#footer p
{
	font-style: italic;
	margin-bottom: 5px;
	text-align: center;
}