try this:
open /includes/functions.php
find (2 times): WHERE i.image_active = 1 AND i.cat_id NOT IN ($cat_id_sql) AND c.cat_id = i.cat_id
replace both with: WHERE i.image_active = 1 AND i.cat_id NOT IN ($cat_id_sql) AND c.cat_id = i.cat_id AND i.image_media_file NOT REGEXP '.*\.(avi|mpg|mpeg|swf|mp3|wav|rm|ram)$'