slider not working, picture not showing up, no function

hi everyone.
really hope someone can help. can’t seem to find the problem with the slider.

it should look and function like this:
https://www.templatemonster.com/demo/32824.html

but it looks like this:
https://www.l-h-dienstleistungen.de

the main image doesnt show and clicking on the thumbnails doesn’t switch the large image.

the “slider.php” is:

<?php $posts_counter = 0; query_posts("post_type=slider&posts_per_page=-1&post_status=publish"); if(have_posts()) { ?>
<div id="slider" class="nivoSlider">
  <?php
		while ( have_posts() ) : the_post(); $posts_counter++;
	?>
  <?php
		$custom = get_post_custom($post->ID);
		$url = get_post_custom_values("slider-url");
		$sl_image_url = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'slider-post-thumbnail');
		$tab_title = get_post_custom_values("tab-title");
	?>
  <?php if(has_post_thumbnail( $the_ID) || $sl_thumb!=""){ ?>

		<?php if($url!=""){ ?>
    <?php echo "<a href='" . $url[0] . "'>";
					echo "<img src='";
					echo $sl_image_url[0];
										echo "' alt='";
					echo $tab_title[0];
					echo "' title='#sliderCaption" . $posts_counter . "' />";
										echo "</a>"; ?>
    <?php }else{ ?>
    <?php echo "<img src='";
					echo $sl_image_url[0];
										echo "' alt='";
					echo $tab_title[0];
					echo "' title='#sliderCaption" . $posts_counter . "' />"; ?>
    <?php } ?>

  <?php } ?>
  <?php endwhile; ?>
  <?php wp_reset_query();?>
</div>
<div class="nivo-controlNav">
	<?php $posts_counter = 0; query_posts("post_type=slider&posts_per_page=-1&post_status=publish"); ?>
<?php
		while ( have_posts() ) : the_post(); $posts_counter++;
	?>
  <?php
		$custom = get_post_custom($post->ID);
		$url = get_post_custom_values("slider-url");
		$sl_image_url = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'slider-small-thumbnail');
		$tab_title = get_post_custom_values("tab-title");
	?>
  <?php if(has_post_thumbnail( $the_ID) || $sl_thumb!=""){ ?>

    <?php echo "<a class='nivo-control' rel='" . ($posts_counter-1) . "'>";
					echo "<img src='";
					echo $sl_image_url[0];
										echo "' alt='";
					echo $tab_title[0];
					echo "' title='#sliderCaption" . ($posts_counter-1) . "' />";
										echo "</a>"; ?>
  <?php } ?>
  <?php endwhile; ?>
  <?php wp_reset_query();?>
</div>
<?php } else { ?>
		<div class="attention-box alert-box" style="margin: 170px 20px 0 20px;">You don't have any <strong>Slides</strong>. You need to create them using <strong>Slides</strong> custom post type.</div>
	<?php } ?>
	<?php wp_reset_query();?>
<?php $posts_counter = 0; ?>
<?php
	query_posts("post_type=slider&posts_per_page=-1&post_status=publish");
	while ( have_posts() ) : the_post(); $posts_counter++;
?>
<?php
	$custom = get_post_custom($post->ID);
?>
<div id="sliderCaption<?php echo $posts_counter ?>" class="nivo-html-caption">
  <?php the_content(); ?>
</div>
<?php endwhile; ?>
<a href="<?php bloginfo('url'); ?>/?page_id=72" class="button slider-button">Mehr</a>
<?php wp_reset_query();?>

can’t seem to find what’s causing the problem.

any assistance would be greatly appreciated. thx