Hello.
I know what your problem is. Using a user account I created only to test this site's Newly Registered Users Restrictions, I logged in and found the button to be missing as well. It is a new user restriction on this site due to you having a low post count. In other-words, an anti-spam feature.
In order to create a "contribution," you need a higher post-count. Probably a minimum of two or three posts. And posts in General Discussion and Test Me don't count to post count either.