Comments and Category Nav. not working

On our blog (www.thejoshdesign.com/blog) our comment function isnt working at all, neither is navigating to posts via category, and we also can’t click on a post to have it pull up on its own page. Another issue is our lack of ability to view posts prior posted that arent on the main page anymore.

Can anyone offer some support? We haven’t done anything with the code since installing it, and even then we didnt make any changes.

THANKS