Sidebar and body "hiding" under header

I am attempting to add a header image using css into my site. I am very new to css so I'm sure I'm missing some incredibly simple tag so that the sidebar and body are adjusted accordingly.

CSS

#sideContainer {float:left;}
.err {
    color: #FF9900;
}

#navMain {
    margin-left:25px;
    color:#999999;
    font-family:Tahoma, Geneva, sans-serif;
}
#headContainer {
    width: 100%;
    position:fixed;
    top:0px;
    height: 150px;
}

#header{
    margin:0px auto;
    height: 150px;
}

#content {
    float:left;
    padding-left: 10px;
    padding-top: 10px;
}

HTML

<HTML>
    <HEAD>
        <?php
            require_once('config.php');
        ?>
        <TITLE>Fund Shui Homepage</TITLE>
        <link rel='stylesheet' type = 'text/css' href = 'default.css' />
    </HEAD>
    <BODY>
        <div id = 'headContainer'>
            <div id = 'header'>
                <?php include 'header.html'; ?>    
            </div>
        </div>
        <div id = 'sideContainer'>
            <div id='navMain'>
                <?php include 'sidebar.html'; ?>
            </div>
        </div>
        <div id = 'content'>

Solution

Just remove the position:fixed. It may be the same with using position:relative.