Shortcodes not working

Hi folks.

Shortcodes are not working on my blog.

I am trying to create a list of all posts within a category, and have tried doing this using various plug ins, all of which use shortcodes, however none work. The shortcode appears in the visual and html tabs of a page, but when viewed in a browser the area of the page is blank.

http://www.north-harbour.co.uk/bikes/used-bikes/

I suspect this is a theme issue, but I don’t know where to start editing the code? I am using the DarkZen theme.

Any help on fixing this, or finding another way to list all posts from a category within a page would be greatly appreciated.

THANKS!