(In reply to comment #102)
> 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.

in the grub menu select the kernel you want to boot and press 'e' then move to
the end of the line that starts:
        linux   /boot/<blah blah blah>
and append the options to the end of that line.  e.g.,
       linux   /boot/<blah blah blah> radeon.modeset=0 1
The '1' means boot into single user mode rather than X.

Also, if you haven't already, try disabling aspm:
       linux   /boot/<blah blah blah> radeon.aspm=0 radeon.dpm=1