Whitescreen at Admin pages after widgetizing theme

I am new to wordpress and have been struggling through creating my own theme. Everything seemed to be going well until I coded the sidebar and widgetized it. The site works perfectly, but in the admin screens, if I post a new post or update a post, I am lead to a blank, white screen. I know that it is due to my theme because when I removed it, I did not get the white screen anymore. I have no plugins installed. What could I have done wrong?

this is the code I added to the functions.php file:

<?php
if ( function_exists('register_sidebar') )
    register_sidebar();
?>

and this is the code I used for my sidebar:

<div id="sidebar">
            <?php if ( !function_exists('dynamic_sidebar') ||
            !dynamic_sidebar() ) : ?>

            <ul>
    <!-- Search -->
                <li id="search" class="widget">
                <?php include(TEMPLATEPATH.'/searchform.php'); ?>
                </li>

    <!-- Recent Posts -->
                <li class="widget">
                    <h2>Recent Posts</h2>
                    <ul>
                        <?php
                        $recent = new WP_Query();
                        $recent -> query('showposts=7');
                        while($recent -> have_posts()) : $recent ->the_post(); ?>
                        <li><a href="<?php the_permalink(); ?>"
                        title="<?php the_title(); ?>"><?php the_title(); ?></a></li>
                        <?php endwhile; ?>
                        </ul>
                </li>

    <!-- Archives -->
                <li id="archives" class="widget">
                <h2>Archives</h2>
                <ul><?php wp_get_archives('type=monthly&limit=7'); ?></ul>
                </li>
    <!-- Categories -->
                <li id="categories" class="widget">
                <h2>Categories</h2>
                <ul>
                <?php wp_list_categories('title_li=&orderby=name'); ?>
                </ul>
                </li>
            </ul>
            <?php endif; ?>
        </div>