Help with multiple dropdown tags search

Does your theme have a search.php to display the results? And if not then create one based on the codex examples or default theme or post the source to your index.php for troubleshooting.

Edit: Your search.php is difficult to debug, try following the structure of a default theme, and put something like this in your search.php to test if that might be the problem:

<?php get_header(); ?>
    <section id="primary" class="site-content">
        <div id="content" role="main">
        <?php if ( have_posts() ) : ?>
            <?php while ( have_posts() ) : the_post(); ?>
                <?php get_template_part( 'content', get_post_format() ); ?>
            <?php endwhile; ?>
        <?php else : ?>
            <article>
                <div class="entry-content">
                    <p>Nothing found, do you want to search?</p>
                    <?php get_search_form(); ?>
                </div><!-- .entry-content -->
            </article><!-- #post-0 -->
        <?php endif; ?>
        </div><!-- #content -->
    </section><!-- #primary -->
<?php get_footer(); ?>