The feed opens instead of posts! Help! :-(

I really hope someone can help … my blog has been up and running smoothly for a while but today, it is impossible to open any of the posts.

The homepage is fine, but when you click on the posts’ title, or ‘read more’ or any of the pages, the blog’s feed appears instead.

The URL is http://www.40ymas.com

Any ideas????

Thanks!