Comment 38 for bug 501323

I suggest you first try to use 'e' to edit the command line in Grub menu when you boot first.
Then if you want to do permanent change:
Oh, reading about Grub2 at: http://doc.ubuntu-fr.org/grub-pc (I speak french too ^^), then I think that the file to be edited is:
gksudo gedit /etc/default/grub
Then edit the line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" and remove the 'noacpi' if it is there.
Then type 'sudo update-grub' in the terminal to update the Grub menu for real.