Forget my previous post. Just reboot, then choose the 'Safe mode' and apply the acpi=off there.
When you are in the actual LL, edit the file (as root) /etc/default/grub
and add the parameters which I suggested in the previous post into it. Save it and run 'update-grub' as root.
If everything goes fine, you don't need to apply safe mode or edit grub any more...
Let me know how it went
