Hi – I have seen this go flaky before.
Create another user, a temporary one. Give it Admin privileges, and log on as that user. See if you can use the visual editor with that temp user. If so, I have resolved this issue before by:
1) BACK UP YOUR DATABASE BEFORE DOING THIS!!!
2) when logged in as the temp user (with visual editor working) delete your actual username. It will ask what you want to do with the posts written by the real user. Move them over to the temp user as their author. Now the temp user is the author of all the posts.
3) Now recreate the real user, and give it Admin privileges. Then log out.
4) Log in as the newly created Real User.
– make sure you can now see/use the visual editor. If so, reverse the process
:delete the temp user
:assign all the posts authored by the temp user to the new real user
If that all works you are back in business.
I haven’t done this enough times yet to learn if there are any implications to deleting the original real user, in terms of lost settings, preferences, etc. – that is why I suggest making a database backup first, so there is a record of how the database was set up prior to making these changes. In the worst case they can be restored.