You have 2 <body> tags (see below): I suggest you move - class="live" - to the first instance and delete the second instance of the <body> tag.
<body>
<div class="container">
<div class="header">
<body class="live">
<nav></nav> is a specific html5 tag and the doctype you are using for the page is NOT compatible.
Change the first 4 lines of your code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
To:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
Note: be aware html 5 tags DO NOT work in IE8 or below. IF you feel the necessity to use them you will need a script to make them compatible.