Fix WYSIWYG-editor on Wordpress-based website

Hi, During work on the site by other workers, somehow the WYSIWYG-editor to add posts to the site (WordPress-based) was corrupted. Therefore, it is not working anymore (does not even show up). I am looking for someone to fix this, so that the employees can use the editor easily to add/edit content to the website. Stuff like formatting that may not work well in the editor (once it shows up) needs to be addressed too. Basically, the editor should be fully functional again and provide no problems in usage. As the site needs to be online at all times, I require you to either make a back-up or to work on your own server. Screenshot: [login to view URL]