Automatisk valg af CSS

Hej,

Nogen som kan fortælle hvorfor mit script giver blank side?


<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>


<SCRIPT LANGUAGE="JavaScript">


<!-- Begin
function redirectCSS() {

if ((screen.width == 640) && (screen.height == 480))
      {document.write("<link href='css/test.css' rel='stylesheet' type='text/css'>")}

else if ((screen.width == 800) && (screen.height == 600))
      {document.write("<link href='css/test.css' rel='stylesheet' type='text/css'>")}

else if ((screen.width == 1024) && (screen.height == 768))
      { document.write("<link href='css/test.css' rel='stylesheet' type='text/css'>")}

else
      {document.write("<link href='css/test.css' rel='stylesheet' type='text/css'>")}
}
// End -->
</script>     
</head>




<body onLoad="redirectCSS()">

<h1>This is a Heading</h1>
<p>This is a paragraph.</p>

</body>
</div>
</html>