You have a number of HTML errors on your main page. Go to settings > writing and select "WordPress should correct invalidly nested XHTML automatically" and then click "save changes."
Now, starting with your latest post, open it in the editor, switch from the visual tab to the HTML tab (waiting for the page to refresh) and then switch back to the visual tag (again waiting for it to refresh), and then click "update post." Check your blog and if it is back to normal (you may have to force refresh the page), you are golden. If not, open the next post and do the same thing till it goes back to normal.