Can't override Search engine

The WordPress search engine in my theme is quite dreadful. It will only search within a category, so most of the time, it produces no results unless I happen to search a word that appears in that category.

I have tried Relevanssi and Search Everything, but these are not overriding the stock search engine. Can someone help me? Here is the code from the search.php:

<?php get_header(); ?>

	<div id="content">
	<?php if (have_posts()) : ?>

		<h2 class="pagetitle">Search Results</h2>

		<div class="navigation">
			<div class="alignleft"><?php posts_nav_link('','','? Previous Entries') ?></div>
			<div class="alignright"><?php posts_nav_link('','Next Entries ?','') ?></div>
		</div>

		<?php while (have_posts()) : the_post(); ?>

			<div class="post">
				<h3 id="post-<?php the_ID(); ?>"><a>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><?php the_title(); ?></a></h3>
				<small><?php the_time('l, F jS, Y') ?></small>

				<div class="entry">
					<?php the_excerpt() ?>
				</div>

				<p class="postmetadata">Posted in <?php the_category(', ') ?> <?php edit_post_link('Edit','','<strong>|</strong>'); ?>  <?php comments_popup_link('Comments are Closed ?', 'Comments are Closed ?', '% Comments are Closed ?'); ?></p> 

				<!--
				<?php trackback_rdf(); ?>
				-->
			</div>

		<?php endwhile; ?>

		<div class="navigation">
			<div class="alignleft"><?php posts_nav_link('','','? Previous Entries') ?></div>
			<div class="alignright"><?php posts_nav_link('','Next Entries ?','') ?></div>
		</div>

	<?php else : ?>

		<h2>Sorry,</h2>
		<p> but your search did not turn up any results.</p>

	<?php endif; ?>

	</div>

<?php get_sidebar(); ?>

<?php get_footer(); ?>