All the content in the backend has dissappeared

Hi, this is relating to site.
I was doing the settings for the ultimate branding plugin and testing this in another browser when suddenly all the content in the backend dissappeared. That is I can see the menu down the left hand side and the admin bar along the top but nothing else at all.
I can click on all the menu items but nothing shows. Just a blank white space.
I appear to have blocked everything out. I tried to remove the ultimate branding plugin via ftp but then I get a white screen with 'you do not have permission to view this site' or something like that so even worse. I have had to contact you thru this site as there is no way of doing this thru the one with the problem.

A little bit stuck now what to do. Can't see anything in the database that would help. The front end seems to be working ok still - I hope anyway. HELP please. Just a bit desperate.