Can't add images, media or links to pages

For a couple weeks now, I haven’t been able to add media or links to any pages. I can do it to posts just fine, and I can edit text in pages just fine.

When I’m editing a page, the Add Media button is there, but nothing happens when I click it. When I try to add a link, the Insert/edit link window opens, I can add the URL, but when I click the Add Link button, it jumps me to the list of all my posts in my dashboard. No link will stick.

I’ve switched over to three different themes to see if it’s a theme problem, but it happens on each of them. I’ve also disabled all my plugins and tried it, but the same thing happens.

Anyone have an idea what’s up?