Question About Uploading files in PHP

["SaEeDoS" <saeedos@xxxxxxxxx>]

Hi all ,
i'm working on a small project , it's about Uploading files .
i put my project online , i have a domain on http://www.parallels.com/
.
The Problem :
when i uploading a file that have a size less than 5 MB it success .
but when the size come large than 5 MB nothing happen , the loading bar of the Browser is completed and nothing happen .
there is No error messages .
the original code must redirect the page to the main page after finishing uploading . 
in my code i didn't determine the maximum size of files .
could any one tell me what the wrong in my code , 
Thanks
#### CODE ####
switch($action)
{
case "upload":
		$dir=$session_user_dir."/";
		if (($_FILES["file"]["size"] < 20000666666600))
	  	{
	  		if ($_FILES["file"]["error"] > 0)
	    {
	    	echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
	    }
	  	else
	    {
	    	header("Refresh: 2; URL=files.php?act=list");	
		    echo "<b>Upload</b>: " . $_FILES["file"]["name"] . "<br />";
		    echo "<b>Type</b>: " . $_FILES["file"]["type"] . "<br />";
		    echo "<b>Size</b>: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />";
		    echo "<b>Temp file</b>: " . $_FILES["file"]["tmp_name"] . "<br />";
	    	if (file_exists("$session_user_dir/" . $_FILES["file"]["name"]))
	      	{
  	echo $_FILES["file"]["name"] . "<b>already exists</b>";
	      	}
	    	else
	      	{    		
		  move_uploaded_file($_FILES["file"]["tmp_name"],
		  $dir. $_FILES["file"]["name"]);
		  $filePath=$dir.$_FILES["file"]["name"];
		      insertFile($_FILES["file"]["name"],$_FILES["file"]["type"],$_FILES["file"]["size"],$filePath);
		      echo "<b>uploading File success</b><br />";
		      echo "Stored in: " .$dir. $_FILES["file"]["name"];
		      $fileName=$_FILES["file"]["name"];
		      $fileType=$_FILES["file"]["type"];
		      $fileSize=$_FILES["file"]["size"];
		      $currentUser=$session_fname." ".$session_lname;
		      $uploadDate=time();
		      sendMail($fileName,$fileType,$fileSize,$currentUser,$uploadDate);
	      	}
	    }
	  	}
		else
	  	{
	  		header("Refresh: 2; URL=files.php");
			echo "Invalid file";
	  	}
	  
	  	/** echo "<script type=\"text/javascript\">
		window.location = \"files.php\"
		</script>"; **/
	break;
}