Wordpress 404.php Title

[admin]

I'm Turkish blogger. I have a wordpress blog. My blog's 404.php page's title is "nothing found for %value%" and i want to change it. I can't change it from title tag in header.php. So how can I?

<a href="http://t1310.hizliresim.com/1g/f/tjzwp.jpg" rel="nofollow">image of problem</a>

this is my code between head tags

    <link rel="stylesheet" type="text/css" href="<?php bloginfo('template_url'); ?>/css/fontello.css" />
<script type="text/javascript" src="<?php bloginfo('template_url'); ?>/js/jquery.min.js"></script>
<meta http-equiv="Content-Type" content="<?php bloginfo('html_type'); ?>; charset=<?php bloginfo('charset'); ?>" />
<title>
    <?php 
        if( is_404() ) {
            echo 'Error 404 - Page Not Found | '; // or Whatever you want
            bloginfo('name');
        }
        else
        { 
          wp_title( '|', true, 'right'); //bloginfo('name'); ?> <?php if ( is_single() ) { ?> » <?php } ?> <?php wp_title();
        }
    ?>
  </title>
<meta name="keywords" content="" />
<meta name="description" content="" />
<meta name="robots" content="index, follow" />
<?php wp_get_archives('type=monthly&format=link'); ?>
<link rel="alternate" type="application/rss+xml" title="RSS 2.0" href="<?php bloginfo('rss2_url'); ?>" />
<link rel="alternate" type="text/xml" title="RSS .92" href="<?php bloginfo('rss_url'); ?>" />
<link rel="alternate" type="application/atom+xml" title="Atom 0.3" href="<?php bloginfo('atom_url'); ?>" />
<link rel="pingback" href="<?php bloginfo('pingback_url'); ?>" />
<link rel="profile" href="http://gmpg.org/xfn/11" />
<?php if ( is_singular() ) wp_enqueue_script( 'comment-reply' ); ?>
<link rel="stylesheet" type="text/css" media="all" href="<?php bloginfo('stylesheet_url'); ?>" />
<link rel="shortcut_icon" href="<?php bloginfo('template_url'); ?>/css/img/favicon.ico" />
<?php wp_head(); ?>