Hi
In the theme's index.php file, this is the code that is causing only the headings to appear, lines 36 to 40
<?php if (!(is_tag()) && !(is_category())){ ?>
<div class="entry">
<?php the_content(__('</p><p>Read More >></p>', 'pyrmont_v2')); ?>
<div class="clear"></div>
</div><!-- end entry -->
<?php } ?>
It says, if this is not a tag page and not a category page, display the post contents. If you want the full contents displayed on all those posts, remove the first and last lines in that block of code.
But that is going to make a very long page. You might consider displaying just the content summary rather than the full content on those tag and category pages. if you want to try that, change that code above to this:
<div class="entry">
<?php if ( is_tag() || is_category() ) {
the_excerpt();
} else {
the_content(__('</p><p>Read More >></p>', 'pyrmont_v2'));
} ?>
<div class="clear"></div>
</div><!-- end entry -->