Er gebeurt niks na submit

<?php
include('../config.php');

  if ($_SERVER['REQUEST_METHOD'] != "POST"){
    
    $select= mysql_query("SELECT * FROM systemen WHERE systeem_id= '1'");
    $row= mysql_fetch_object($select);
    ?>
    <form method="POST" action="systemen_admin.php">
    <table width="80%" border="0" cellspacing="0" cellpadding="0">
      <tr>
        <td width="25%">Behuizing:</td>
		<td width="75%"><input type="text" name="behuizing" value="<?php echo $row->behuizing; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Processor:</td>
		<td width="75%"><input type="text" name="processor" value="<?php echo $row->processor; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Moederbord:</td>
		<td width="75%"><input type="text" name="moederbord" value="<?php echo $row->moederbord; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Geheugen:</td>
		<td width="75%"><input type="text" name="geheugen" value="<?php echo $row->geheugen; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Diskette:</td>
		<td width="75%"><input type="text" name="diskette" value="<?php echo $row->diskette; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Harde Schijf:</td>
		<td width="75%"><input type="text" name="hardeschijf" value="<?php echo $row->hardeschijf; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">DVDRom:</td>
		<td width="75%"><input type="text" name="dvdrom" value="<?php echo $row->dvdrom; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">DVD Rewriter:</td>
		<td width="75%"><input type="text" name="dvdrewriter" value="<?php echo $row->dvdrewriter; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Grafische Kaart:</td>
		<td width="75%"><input type="text" name="grafischekaart" value="<?php echo $row->grafischekaart; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Muis:</td>
		<td width="75%"><input type="text" name="muis" value="<?php echo $row->muis; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Toetsenbord:</td>
		<td width="75%"><input type="text" name="toetsenbord" value="<?php echo $row->toetsenbord; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Usb:</td>
		<td width="75%"><input type="text" name="usb" value="<?php echo $row->usb; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Netwerkkaart:</td>
		<td width="75%"><input type="text" name="netwerkkaart" value="<?php echo $row->netwerkkaart; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Scherm:</td>
		<td width="75%"><input type="text" name="scherm" value="<?php echo $row->scherm; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Software:</td>
		<td width="75%"><input type="text" name="software" value="<?php echo $row->software; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Speakers:</td>
		<td width="75%"><input type="text" name="speakers" value="<?php echo $row->speakers; ?>"</td>
	  </tr>
	  <tr>
        <td width="25%">Prijs:</td>
		<td width="75%"><input type="text" name="prijs" value="<?php echo $row->prijs; ?>"</td>
	  </tr>
	  <tr>
	    <td colspan="2" width="100%"><input type="submit" name="submit" value="Aanpassen"></td>
	  </tr>
	</table>
	</form>
  <?php	
  }
  else {
    
    $behuizing= ($_POST['behuizing']);
	$processor= ($_POST['processor']);
	$moederbord= ($_POST['moederbord']);
	$geheugen= ($_POST['geheugen']);
	$diskette= ($_POST['diskette']);
	$hardeschijf= ($_POST['hardeschijf']);
	$dvdrom= ($_POST['dvdrom']);
	$dvdrewriter= ($_POST['dvdrewriter']);
	$grafischekaart= ($_POST['grafischekaart']);
	$muis= ($_POST['muis']);
	$toetsenbord= ($_POST['toetsenbord']);
	$usb= ($_POST['usb']);
	$netwerkkaart= ($_POST['netwerkkaart']);
	$software= ($_POST['software']);
	$scherm= ($_POST['scherm']);
	$speakers= ($_POST['speakers']);
	$prijs= ($_POST['prijs']);
	
	$update = mysql_query("UPDATE systemen SET behuizing= '" .$behuizing. "', processor= '" .$processor. "', 
	moederbord= '" .$moederbord. "', geheugen= '" .$geheugen."', diskette= '" .$diskette. "', 
	hardeschijf= '" .$hardeschijf ."', dvdrom= '" .$dvdrom. "', dvdrewriter= '" .$dvdrewriter. "', 
	grafischekaart= '" .$grafischekaart."', muis= '" .$muis. "', toetsenbord= '" .$toetsenbord. "',
	usb= '" .$usb. "', netwerkaart= '" .$netwerkkaart. "', software= '" .$software."', scherm= '" .$scherm. "',
	speakers= '" .$speakers."', prijs= '" .$prijs. "' WHERE systeem_id= '1'");
	
	echo 'Uw aanpassingen zijn succesvol uitgevoerd.';     
  }  

?>