Be sure to check the code in a validator. This code passes:
Code:
<!DOCTYPE html>
<html>
<head>
<title>Oldham Athletic Blog!</title>
<link rel="stylesheet" type="text/css" href="css/style.css">
</head>
<body>
<div id="wrapper">
<div id="header">
<h1>Oldham Athletic Blog</h1>
<h2>The life of an Oldham fan</h2>
</div>
<ul id="nav">
<li><a href="index.html">Home</a></li>
<li><a href="#">Videos</a></li>
<li><a href="#">Our History</a></li>
<li><a href="#">Contact Us</a></li>
<li><a href="#">Forum</a></li>
</ul>
<div id="content">
<div class="post">
<h3>First Post</h3>
<img src="images/nottingham_win.jpg" class="pic1" alt="nottingham"/>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse ultrices mollis eros, nec laoreet sapien bibendum vitae. In at iaculis ipsum. Nunc vitae tortor vitae elit molestie porttitor quis nec justo.</p>
</div>
<div class="post">
<h3>Second Post</h3>
<img src="images/baxter_dickov.jpg" class="pic2" alt="baxter"/>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse ultrices mollis eros, nec laoreet sapien bibendum vitae. In at iaculis ipsum. Nunc vitae tortor vitae elit molestie porttitor quis nec justo.</p>
</div>
<div class="post">
<h3>Third Post</h3>
<img src="images/new_badge.jpg" class="pic3" alt="badge"/>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse ultrices mollis eros, nec laoreet sapien bibendum vitae. In at iaculis ipsum. Nunc vitae tortor vitae elit molestie porttitor quis nec justo.</p>
</div>
</div>
<div id="sidebar">
<div class="section">
<h3>Latics to play Liverpool!</h3>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nullam ultrices lacinia elit eget placerat. Nullam aliquet, erat ac auctor placerat.</p>
</div>
<div class="section">
<h3>Too early for Daniel Taylor?</h3>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nullam ultrices lacinia elit eget placerat. Nullam aliquet, erat ac auctor placerat.</p>
</div>
<div id="logo">
<img src="images/new_badge.jpg" alt="badge"/>
</div>
</div>
</div>
</body>
</html>
Your CSS has one extra closing brace as well.