Comment 4 for bug 1077975

Explanations for Clara - how to login to the system affected by this bug.

(Re)boot your system, holding down the "Shift" key - the GRUB menu will appear.
In the GRUB menu select
"Advanced options for Ubuntu"
then
"Ubuntu, with Linux X.Y.Z-N-generic (recovery mode)"
(X.Y.Z-N is a kernel version number, choose any version, the latest one will be fine).
In the "Recovery menu" choose
"root Drop to root shell prompt"
You get the root shell, but filesystem is mounted read-only. Remount it read-write with the command like
mount -o remount,rw /

Now you can do what you like, for example,
vi /usr/share/X11/xorg.conf.d/91-noaccel.conf
and type the configuration lines I mentioned in my first post.
Instead of
 Option "NoAccel"
you may also try
 Driver "vesa"
- it is not as fast as native drivers, but supposed to work with most graphics cards.