Navigate to "/boot/grub/menu.lst" and open that file. Toward the bottom of the page you will see a line like this:
## ## End Default Options ##
After that you will see several lines together that constitute your primary boot stanza. One of those will look something like this:
kernel /boot/vmlinuz-2.6.22-14-generic root=/dev/sda2 ro quiet splash
Add a space and "acpi=off" right after the "quiet splash". No quotes.
Save the file and exit. Be careful and try not to make a typo.
See if that helps you.