I am having the same problem after upgrading to WordPress 3.3.1.
There are no editing icon available in the visual mode, so I cannot edit both pages & posts in visual mode. I can edit post & pages using the HTML code. The HTML code is also appearing in the visual edit mode.
You can see it when you highlight the text.See attached The password testpage123.
The HTML editor is working ok and the page displays correctly in the browser.
I have tested to ensure that it is not theme related by temporarily switching to the default WordPress theme and clearing the cache. However this does not fix the problem.
I have also tested plugins by deactivating and reactivating them individually. However, this does not solve the problem.
My conclusion is that there is a bug in WordPress 3.3.1 base code.
Could you please investigate and advise