Add Media and other plugins not working in visual editor

Sometime yesterday the “add media” button, the WordPress Jetpack form builder, and the buttons for a few of my plugins (Shortcodes Unlimited, Drop Shadow Boxes) stopped working entirely in the page/post visual editor.

When I click on any of these buttons in the visual editor, the URL in my browser changes like it’s trying to work, but NOTHING happens.

I’ve tried deactivating every single plugin, and then going back to see if the “add media” button would work, but nothing had changed. I reactivated my plugins and the same thing is still happening.

I’ve tried re-installing WordPress 3.5. Didn’t help.

I have the same theme and the same plugins running on a different WordPress site, and those work fine.

Any suggestions? I have no idea what else to do.