All of my pages, except the home page, are coming up with 404 errors, and I can't figure out why. All the slugs are correct, the pages have been published for years, and all of the sudden they can't be loaded.

The URL is http://www.blackberrymorganhorses.com/

I'm running WP 4.2.2, Atahualpa 3.7.24.

I've tried disabling all the plugins and switching to a default theme, but the pages still will not come up.

Any ideas please?

Try changing your permalinks to Default and save. Then switch back to Post name and save.

OMG, thank you, that worked. Didn't even think of that