Posts will not publish

Just upgraded to 2.8.2 this week.

I started writing a post today, and while I was in the process of doing that, my admin login cookie expired. Thus, when I went to publish the post, it simply vanished and I got dropped into the Edit Posts page. It took me a while to figure out what had happened, but after I fixed the login, refreshed the page and cleared the cache, the problem still remained. I have tried repeatedly but cannot get a post (any post, not just that first one) to publish. I cleared the cache again (Firefox) and even shut down and restarted the browser on the off chance something had happened to it. I shut down and reactivated my plugins in case one of them was causing the problem. I am out of ideas. Couldn’t find this exact problem in a search.