Disappearing editor control in WordPress pages editor

[Frank S.]

If you encounter a situation where the visual/html page editor does not show up or work properly then you should read the solution below:

html/visual is a function of WordPress and nothing to do with nor controlled by themes. If you go into WP-admin and select Users/Your Profile/ You'll see right at the top of the page in "Personal Options" an entry field that says: "Visual Editor [] Disable the visual editor when writing"
If that box is checked you will lose control in your editor.
Apart from that,.. sometimes it can be caused by a plugins conflict in which case you can try installing an independent mce editor from the free WP plugins directory called "tinymceAdvanced" and that should do the job!