When I upgraded my site to WordPress 3.5.1 the visual editor no longer allowed input and was just basically a unusable blank white box. I could use the text tab if I selected it and then refreshed the page.
So I first tried de-activating all plugins and setting the them back to 'Twenty Eleven' with no success. Finally after checking the console errors in IE I saw:
LOG: Failed to load: http://localhost/blog/wp-includes/js/tinymce/langs/en.js
LOG: Failed to load: http://localhost/blog/wp-includes/js/tinymce/themes/advanced/langs/en.js
So I went to http://www.tinymce.com/ and download the latest version. The I just copied the en.js file to the folders listed above and I had to create a 'langs' folder for the second one to stick en.js into.
Now my visual editor works great and I hope this can help others with the same problem!