“Fatal error: Call to undefined function get_header()…”

I’m working on a site (https://jennifer.coffeeismagic.com/) and, when I was initially formatting WordPress I didn’t want that many features so I stripped out all the <?php get_sidebar() ?> stuff. I realized after the fact that I actually wanted the sidebar on the front page so I stuck that bit of code back in on the archive.php and archives.php files, right where it was before, above get_footer — to no effect. So I decided to stick <?php get_sidebar() ?> back into the index.php file and when I did that it totally crashed the site, saying “Fatal error: Call to undefined function get_header() in /home/christian_d/jennifer.coffeeismagic.com/index.php on line 1”. I didn’t change anything other than adding get_sidebar and when I took it back out it still gives me that error. The header.php file is still intact in the same place it was on the server so i don’t know what’s going on. Any ideas are much appreciated!

Here is the code of index.php:

<?php get_header() ?>

	<div id="container">
		<div id="content">

			<div id="nav-above" class="navigation">
				<div class="nav-previous"><?php next_posts_link(__( '<span class="meta-nav">&laquo;</span> Older posts', 'sandbox' )) ?></div>
				<div class="nav-next"><?php previous_posts_link(__( 'Newer posts <span class="meta-nav">&raquo;</span>', 'sandbox' )) ?></div>
			</div>

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

			<div id="post-<?php the_ID() ?>" class="<?php sandbox_post_class() ?>">
				<h2 class="entry-title"><a href="<?php the_permalink() ?>" title="<?php printf( __('Permalink to %s', 'sandbox'), the_title_attribute('echo=0') ) ?>" rel="bookmark"><?php the_title() ?></a></h2>
				<div class="entry-date"><abbr class="published" title="<?php the_time('Y-m-d\TH:i:sO') ?>"><?php unset($previousday); printf( __( '%1$s – %2$s', 'sandbox' ), the_date( '', '', '', false ), get_the_time() ) ?></abbr></div>
				<div class="entry-content">
<?php the_content( __( 'Read More <span class="meta-nav">&raquo;</span>', 'sandbox' ) ) ?>

				<?php wp_link_pages('before=<div class="page-link">' . __( 'Pages:', 'sandbox' ) . '&after=</div>') ?>
				</div>

			</div><!-- .post -->

<?php comments_template() ?>

<?php endwhile; ?>

			<div id="nav-below" class="navigation">
				<div class="nav-previous"><?php next_posts_link(__( '<span class="meta-nav">&laquo;</span> Older posts', 'sandbox' )) ?></div>
				<div class="nav-next"><?php previous_posts_link(__( 'Newer posts <span class="meta-nav">&raquo;</span>', 'sandbox' )) ?></div>
			</div>

		</div><!-- #content -->
	</div><!-- #container -->

<?php get_footer() ?>