Drag and drop menus not working

The drag and drop feature on the menu admin page worked when I started the project and now it doesn’t. I’ve followed all the suggestions I’ve seen on this forum and on the web: disable plugins (I’ve actually deleted all plugins except for Akismet), different browser, different theme, upgrade WP, fresh manual WP install, but I’m still getting the same behavior. I know this is a common problem, but I can’t think of anything else to do.

Thanks for your insight.