Hi, my HTML Navigation bar (here: http://tridimension.comoj.com/includes/header.php) for some reason sticks to the side of my page, and is reorganizing itself into a vertical line.

HTML Code:
<h4><a href="../index.php">Home</a></h4> | <h4><a href="../forum/index.php">Forum</a></h4> | <h4><a href="../helpful/index.php">Helpful</a></h4> | <h4><a href="../progress.php">Progress</a></h4>
Could anyone identify the problem? I am trying to put it next to the logo, in a horizontal line.