As you may be aware, the Disappearing Visual Editor is an Issue that has haunted WordPress users for quite some time. Using feedback from here and there, my first step was to rename the plugins folder as plugins-old (disabling all plugins). That fixed it.
After some investigation, the guilty plugins turned out to be
1. SB Child List http://wordpress.org/extend/plugins/sb-child-list/description/
2. Page List http://wordpress.org/extend/plugins/page-list/description/
These are lightweight short-code plugins. It is beyond my comprehension how they managed to mess up TinyMCE.
I hope those still suffering from this epidemic may find this helpful. I suffered for six months.