Main page works normally, all content unavailable

My WP site at eleven-thirtyeight.com is showing its main page like normal but if you try to click through to any other content you get a 404 error. The back end still works fine and the files all seem to be there, they’re just inaccessible on the front end. This started happening late in the day yesterday when nothing was being changed or updated as far as I know so I can’t begin to guess what the problem is.

Edited to add: actually, I’ve noticed one other thing–the back end menus do function and all my content is still there but if I try to edit or create a new post it won’t save, and tells me “the response is not a valid JSON response.”

• This topic was modified 4 years, 3 months ago by SteadyUP.

The page I need help with: [log in to see the link]