Schoolboy is absolutely correct. If you use your Developer's Tool kit in the admin and search for tpl_top_nav.php which is being called by a file that may be overriding basic Zen Cart operation.
I don't want to reopen the discussion on whether these templates work well with mods BUT I do think it's necessary to point out that folks should follow the posting tips when posting.
Instead of our having to research and guess, we could have been quicker are more thorough with more information to start with.