In ubuntu 12.04 with noveau driver I modified only
70 GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT"
and fixed for me
In ubuntu 12.04 with noveau driver I modified only
70 GRUB_CMDLINE_ LINUX_DEFAULT= "$GRUB_ CMDLINE_ LINUX_DEFAULT"
and fixed for me