https://bugs.freedesktop.org/show_bug.cgi?id=66963
--- Comment #102 from Eugene ken20001@ukr.net --- If you could explain me where is kernel command line (when I'm seeing GRUB menu push "e" or "c"; and if "c" what to do after I entered radeon.modeset=0 in there?), I would try it. I'm just a newbie using kubuntu a few months.