Could you go to the Tools ... Developers Tool Kit ... and in the bottom input box enter:
category_row
select Catalog ... and click Search ...
Do you see the require statement in 1 or more files:
Code:
require($template->get_template_dir('tpl_modules_category_row.php',DIR_WS_TEMPLATE, $current_page_base,'templates'). '/tpl_modules_category_row.php');
and is one of them commented out:
Code:
// require($template->get_template_dir('tpl_modules_category_row.php',DIR_WS_TEMPLATE, $current_page_base,'templates'). '/tpl_modules_category_row.php');
If so, what happens if you fix that file and remove those comment marks?