Comment form missing

In your theme file, you’ll have to add:

<?php comments_template(); ?>

where you want the comments to go.

In the index.php file within the folder of the theme I’m using, the above line is already there. Does it need to be somewhere else?

<div class="post">
<h3 class="storytitle" id="post-<?php the_ID(); ?>"><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link: <?php the_title(); ?>"><?php the_title(); ?></a></h3>
<div class="meta"><?php _e("Filed under"); ?> <?php the_category(); ?>&nbsp;by <?php the_author(); ?> — <?php the_time('m/d/Y'); ?> @ <?php the_time(); ?> <?php edit_post_link(); ?></div>
<div class="storycontent">
<?php the_content(); ?>
</div>
<div class="feedback">
<?php wp_link_pages(); ?>
<?php comments_popup_link(__('Comments (0)'), __('Comments (1)'), __('Comments (%)')); ?>
</div>
<!--
<?php trackback_rdf(); ?>
-->
<?php comments_template(); ?> <---------
</div>
<?php endforeach; else: ?>
<p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
<?php endif; ?>
</div>

Do you also have a single.php and/or page.php? If you do, it’ll need to go in there.

There’s a page-new.php in wp-admin. Is that the one you mean? The entire document consists of the code below:

<?php
require_once('admin.php');
$title = __('New Page');
$parent_file = 'post.php';
require_once('admin-header.php');

get_currentuserinfo();
?>

<?php if ( isset($_GET['saved']) ) : ?>
<div class="updated"><p><strong><?php _e('Page saved.') ?> <a href="edit-pages.php"><?php _e('Manage pages'); ?> &raquo;</a></strong></p></div>
<?php endif; ?>

<?php
if ($user_level > 0) {
$action = 'post';
get_currentuserinfo();
//set defaults
$post_status = 'static';
$comment_status = get_settings('default_comment_status');
$ping_status = get_settings('default_ping_status');
$post_pingback = get_settings('default_pingback_flag');
$post_parent = 0;
$page_template = 'default';

include('edit-page-form.php');
}
?>

<?php include('admin-footer.php'); ?>

No, don’t edit anything in wp-admin. Or in wp-includes, for that matter.