Sorry to hear of the problem you are having.
It seems latest WordPress version related issue as described here https://wordpress.org/support/topic/wordpress-4-8-editor-failed-to-load-content-css/
Would you mind if i log in to your site and do some troubleshooting? If this is ok then could you please share me your site log in details privately by adding them in the box having text “Click here to share private content. Only you and forum moderators will bee able see it.”?