I've just had a look at my BIOS and i've got ACPI disabled, and mine shuts down automatically...
Hmmm puzzling..
My APM is enabled though.
Just found this in "help & support centre":-
The APM tab is unavailable on ACPI-compliant computers. ACPI automatically enables Advanced Power Management, which disables the APM tab.
Also this:-
During Windows Setup, ACPI is installed only if all components present during Setup support power management. Some components, especially legacy components, do not support power management and can cause erratic behavior with Advanced Power Management (APM), or may prevent ACPI from being installed. Examples of such components are Industry Standard Architecture (ISA) components and an out-of-date BIOS.
So judging by that, i'd of thought you do have ACPI installed, because you've no APM tab...
Put ACPI in the search field in the help & Support Centre; it throws up quite a lot. Have a look there.
This is getting more confusing...
I don't know much really about computers so i'll stop here and let someone else have a go...
Anyone???