<?php
$siteadi= addslashes( $_POST['siteadi'] );
if
($_POST[kaydet]){
   $user=mysql_query("update ayarlar set site_adi=$siteadi");
   echo "Ayarlar basariyla kaydedildi !";
exit(); }
$user=mysql_fetch_array(mysql_query("select * from ayarlar")); 
?>
<form action="" method="post">
<input type="hidden" name="opt_save" value="1">

<table width="45%" cellpadding="2" cellspacing="2"><tr>
<td class="c" colspan="2"><p align="center"><font size="4" color="#00CCFF"><b>Ayarlar</b></font></td></tr>
<tr>
<th align="left" width="28%">Site Adı</th><th width="30%" align="right">
<input name="siteadi"  size="50" type="text" maxlength="60" value="<?= $user['eklenecek_metal'] ?>"></tr>
<tr><th width="28%">&nbsp;</th><th width="30%">
<input type="submit" name="kaydet" value="Ayarlari Kaydet" /></tr></form>
    </table>
böyle deneyin. ayrıca veritabanına bağlantı kurdunuz mu ?