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, make one minor change such as adding and then deleting a space, and then click "update post." Check your blog and if it is back to normal, you are golden. If not, open the next post and do the same thing till it goes back to normal.

A recent post appears on sidebar of screen where widgets should be. Please fix formatting.
Blog url: http://jrfibonacci.wordpress.com/