On the editing part (say add a post or add a page), I am unable to change from Visual to Text and the Add Media does not work. Also, I am unable to edit widgets if I disable accessibility mode. Any clues why? I have latest Atahualpa version and latest Wordpress version... I have several websites using Atahualpa and several browsers and the same happens in all of them. Any clues?

no way to tell - you need to do some digging, look at error logs, remove plugins, swap themes to narrow down what can work