Editing box is blank – unable to edit pages and posts

The WordPress editing box has gone blank – there are no menu icons above the editing box, and the text is not displaying in either visual or text view, but if you highlight the text, you can see it’s there (see screenshot of issue: http://imgur.com/pebEac7)

This issue popped up a year or two ago and one of the solutions was to install the “Use Google Libraries” plugin. This is no longer working.

I have done all the normal troubleshooting procedures — switched to the twenty fifteen theme, disabled all plugins, re-installed wordpress, etc, and still having the same issue.

Any ideas? I’m using WordPress 4.3.1