No, that’s not it. Tried deleting everything out of /wp-content/plugins, and I get the same result.
Is there any sort of switch in PHP that I could set to make it display error messages if there are any? I tried
error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);
in wp-admin/post.php, and saw no error message, either on the page, or in the logs. I don’t know much PHP. Anything else I could try?