[O] src blocks not fontified

[Shiyuan]

Hi, 

    I am using Emacs 24.3 with the built-in org mode(7.9.3). The src code block is not fontified (Emacs is started with -Q option)  

#+BEGIN_SRC emacs-lisp

    (defun org-xor (a b)

      "Exclusive or."

    (if a (not b) b))

#+END_SRC

This is my first time to use org-mode, so I could miss some setup steps.Do I need to do any setup in my .emacs if I just use the built-in org? 

Thanks. 

Shiyuan