Formatting disappearing in posts

All formatting disappears when a post is displayed in the blog. So there are no paragraphs or bold text or italic text or anything like that. Just one big lump of a paragraph.

This is a problem, particularly if one wants most of the post to appear on the front page. If, say, I have a blog with lots of news.

I’m not a programmer, but it seems to be coming from the loop.php which loads content using:
<?php supernova_content(); ?>
which strips all the formatting.

Replacing that code with something like:
<?php the_content(); ?>
retains all the formatting, but also loads an additional thumbnail image (so there are two!).

I considered using this version and deleting the code which pulls in the thumbnail in loop.php (<?php supernova_thumbnail(get_the_ID()); ?>), but this loses the nice border around the featured image and is probably too much playing around with the code for a non-programmer.

At the moment, I am having to live with this lack of formatting on my posts. But would love to know if you are able to fix this.