Won’t look for category.php or archive.php

When I click on a category, the page seems to skip over “archive.php” and chooses “index.php” so I always see the exact same homepage when I choose a category. I cleared archive.php just to make sure it was being ignored, and the same thing happened.

I made this blog a few days ago and am working with a theme (made by someone else; http://wpjunction.com/magazine/) I just went to the theme demo page and realized that even the demo page has the same problem, so I am not sure where to go from here. This is what archive.php looks like, straight from the theme pack:

<?php
/**
 * ProMag Theme
 * Designed by HPA
 * Coded by misbah (ini_misbah@yahoo.com)
 */
get_header();?>
				<div id="content">
					<?php if (have_posts()) : ?>

					<?php $post = $posts[0]; // Hack. Set $post so that the_date() works. ?>
					<?php /* If this is a category archive */ if (is_category()) { ?>
					<h2 class="pagetitle">Archive for the ‘<?php single_cat_title(); ?>’ Category</h2>
					<?php /* If this is a tag archive */ } elseif( is_tag() ) { ?>
					<h2 class="pagetitle">Posts Tagged ‘<?php single_tag_title(); ?>’</h2>
					<?php /* If this is a daily archive */ } elseif (is_day()) { ?>
					<h2 class="pagetitle">Archive for <?php the_time('F jS, Y'); ?></h2>
					<?php /* If this is a monthly archive */ } elseif (is_month()) { ?>
					<h2 class="pagetitle">Archive for <?php the_time('F, Y'); ?></h2>
					<?php /* If this is a yearly archive */ } elseif (is_year()) { ?>
					<h2 class="pagetitle">Archive for <?php the_time('Y'); ?></h2>
					<?php /* If this is an author archive */ } elseif (is_author()) { ?>
					<h2 class="pagetitle">Author Archive</h2>
					<?php /* If this is a paged archive */ } elseif (isset($_GET['paged']) && !empty($_GET['paged'])) { ?>
					<h2 class="pagetitle">Blog Archives</h2>
					<?php } ?>
					<?php while (have_posts()) : the_post(); ?>
						<div class="post" id="post-<?php the_ID(); ?>">
							<h2 class="title"><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>
							<div class="meta">
								<p>
									<span class="datepost"><?php the_time('l, F jS, Y') ?></span>
									<span class="commented"><?php comments_number('No Commented','one Commented','% Commented'); ?></span>
								</p>
								<p>
									<span class="tagpost"><?php the_tags( 'Under : ', ', ', ''); ?></span>
								</p>
							</div>
							<div class="entry">
								<?php the_content(); ?>
							</div>
						</div>
					<?php endwhile; ?>
					<?php else : ?>
					<?php get_search_form(); endif; ?>
					<div class="clear"></div>
				</div><!-- /content -->
<?php get_sidebar(); get_footer(); ?>

Is there something I can put into index.php to force it to recognize archive.php when I choose one category?