Formidable broke my website and now uninstall won’t work

I’ve installed Formidable Forms on a customers site. Upon completing the install, the Formidable Menu in the admin areas seems to work OK, but most of the rest of my admin area is broken. Most of the links now (including Pages, Comments, Media, Settings, Plugins, etc.) just give me a server error. So i’ve found the Uninstall button on the Formidable > Settings page. However, when i click this, i just get a spinning circle symbol and nothing seems to happen. This is pretty desperate now and I need to get the customers site up and running urgently.