Blank page when clicking on a Page on navigation.

Hi!
I recently did some changes to the code to fix some errors, and now have a bigger problem I can’t solve:

I have navigation tabs that direct to a Page (the site is not a blog). Now whenever I click on a tab, it returns a blank page.
https://www.rsyke.net

Any ideas what could be the problem?

I’m guessing the problem has something to do with this:

<li><h2>Alaosiot</h2>
<ul><?php
if($post->post_parent)
$children = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0"); else
$children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0");
if ($children) { ?>

<?php } ?>
</ul>
</li>

This opened the submenu to the sidebar.

I have the stuff from the template on the sidebar.php still, should I remove this stuff?

<?php 	/* Widgetized sidebar, if you have the plugin installed. */
if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar() ) : ?>

<?php if ( is_404() || is_category() || is_day() || is_month() || is_year() || is_search() || is_paged() ) {?> <li>

<?php /* If this is a 404 page */ if (is_404()) { ?>
<?php /* If this is a category archive */ } elseif (is_category()) { ?>
<p>Selaat <?php single_cat_title(''); ?> kategoriaa.</p>

<?php /* If this is a yearly archive */ } elseif (is_day()) { ?>
<p>Selaat <a href="<?php bloginfo('url'); ?>/"><?php echo bloginfo('name'); ?></a> arkistoa, sivu luotu <?php the_time('l, F jS, Y'); ?>.</p>

<?php /* If this is a monthly archive */ } elseif (is_month()) { ?>
<p>Selaat <a href="<?php bloginfo('url'); ?>/"><?php echo bloginfo('name'); ?></a> arkistoa <?php the_time('F, Y'); ?>.</p>

<?php /* If this is a yearly archive */ } elseif (is_year()) { ?>
<p>Selaat arkistoa <a href="<?php bloginfo('url'); ?>/"><?php echo bloginfo('name'); ?></a> vuodelta <?php the_time('Y'); ?>.</p>

<?php /* If this is a monthly archive */ } elseif (is_search()) { ?>
<p>Etsit sivuston<a href="<?php echo bloginfo('url'); ?>/"><?php echo bloginfo('name'); ?></a> arkistosta <strong>'<?php the_search_query(); ?>'</strong>.</p>

<?php /* If this is a monthly archive */ } elseif (isset($_GET['paged']) && !empty($_GET['paged'])) { ?>
<p>Selaat <a href="<?php echo bloginfo('url'); ?>/"><?php echo bloginfo('name'); ?></a> arkistoa.</p>

<?php } ?>

Any articles on blank pages weren’t resolved. Hope this will be. I can explain the situation more, if necessary.