Comment 20 for bug 307645

well, its good that acpi=off works but this option should not be added directly to the grub.cfg file.
The problem is whenever there will be upgrade, the option will be lost. Moreover you will also see at the start of grub.cfg file *do not edit this file*.
If you want to add acpi=off to your options then edit /etc/default/grub file.
In this file there will be an option like :
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
just add acpi=off after splash so that it will look like :
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=off"

and then don't forget to give the command :
sudo update-grub

@Phil Ferrar : do you mean grub.cfg instead of boot.cfg. In my system there is no such file named boot.cfg in /boot/grub directory. If you mean grub.cfg then dont try to edit it directly.