I have a same problem, my visual editor was not appear on my screen, just html editor. I am using Chrome when I got that problem. But, when I switch my browser to Firefox, I didn’t get any problem with visual editor.
Unfortunately, 2.7b3 did not work well for me. I was upgrading it from version 2.6.3. So, when I type in my address bar mydomain.com/wp-admin/, it’s work. But when I want to login to my Dashboard, it give me a 404 page. Can I downgrade it to 2.6.3 again?
I upgrade it with remove my wp-admin and wp-include folder and then I copy the 2.7 beta 3 to my public_html to replace the old one.
I have a problem that similar with this problem. I was upgrading my WP 2.6.3 to 2.7 beta 3. After I was login and enter my user and password, I bring to 404 page. I am using permalink domainname.com/postname/
Anyone can help me?