have you loaded the drivers for the bios fuctions namely apm or acpi? which of both do you use? how old is your notebook, i.e. was it born in acpi era? does the machine hang or print an error message instead of powering off or does it just not know how to power off? i don't know if this happens with power off, but some bioses are buggy and don't execute or advertise functions, habe you checked your bios version?