404 errors

I am getting 404 errors from my installation of classifieds.

The URL(s) in question are :

http://artisttab.com/index.php/classifieds/
http://artisttab.com/index.php/classifieds/checkout/
http://artisttab.com/index.php/classifieds/my-classifieds/

The root domain is artisttab.com, the pages seem to be there as far as wp-admin goes, but it does not show on the wesbite.

Also, is there a way to use a widget to display classified ad categories?