edit page has squashed into two small columns

Hello. Please Help, I probably need to change a size setting but I don’t know where . . .

I have developed a small problem with the editing page for posts and pages, in my admin area. It appears that the 1st of the two columns has shrunk down to about 30 instead of 700 or something around there. So I cannot use the page. Any ideas please? All other dash and plugins are ok. it effects all users, url
http://www.cloudfree-horizons.co.uk