ok, I’ve been dealing with this too and it’s been driving me crazy. some of my wp sites are fine while others are having the same issues. after everything else I ran across an older success story on this issue where they ended up deleting their browser history and closing and reloading their browser. That didn’t work for me, BUT I do use Firefox a lot and so I tried using my explorer and wow… it worked… so maybe try a different browser.
It seems that there are a lot of people with this issue and large number of ways for this problem to be created. The hard part is trying to find the problem and solution that fits yours. It’s like there is one issue, 50 ways to create that issue and about 40 of them have solutions, each very specific to each problem.
If this doesn’t work, keep looking! Here are other threads with this issue and the many solutions and ideas for all of these problems that have the same issue:
http://ww.wp.xz.cn/support/topic/visual-editor-disappearing-1?replies=12
http://ww.wp.xz.cn/support/topic/visual-editor-lost-after-upgrade-to-30?replies=18
http://ww.wp.xz.cn/support/topic/visual-editor-notes-solution-for-fixing?replies=1
