I really thought I had posted this earlier today, but I don't see it in my admin panel, so please delete (or merge) if there is, in fact, an earlier instance.
As of yesterday, my visual editor toolbar is missing. The media buttons (add image, etc.) are present, but don't do anything. If I switch to HTML mode, I cannot switch back.
I have tried disabling all plugins and switching to the default or Twenty-Eleven themes, to no avail. I upgraded (manually) to WP 3.2.1 (was using 3.2 before, I think), and still no effect. I re-uploaded the wp-admin and wp-includes folders. No change.
I suspect that the problem was initially caused either by the installation of a plugin (which was later removed - I tested a number of plugins yesterday) or by the failed attempt to auto-upgrade all upgradable plugins. (That process locked up.)
Having dug through quite a few old posts on this forum, I found one that suggested visiting this page to check for errors:
That page says "File not Found." I assume that could be a problem. (Unless the method for displaying this stuff has changed since 3.1.)
Thing is, that file IS there. I can see it in my ftp/Control Panel.