404 not working

does your theme have a 404.php?

if not, make one and drop in this code or similar

<?php get_header(); ?>

	<div id="content">

	<div class="post">

	<span class="breadcrumbs"><a href="<?php echo get_option('home'); ?>/">Home</a> &raquo; 404 Not Found</span>

	<h2 class="title">Error 404 - Not Found</h2>

		<div class="entry clearfloat">
		<p>Ooops, I cannot find you the page you are looking for. You may try to search my site another keyword or use the navigation on your right to browse my site.</p>

		</div>

	</div>

	</div>

<?php get_sidebar(); ?>
<?php get_footer(); ?>