you have moved your mouse, time to reboot
Now this isn't from an official source or anything, but while trying to sort out a problem on Mom's computer I found this piece on APM/ACPI support in Windows 2000:
An installation gotcha!: APM support must be enabled in the BIOS when Windows 2000 is installed. A non-ACPI system that has APM disabled in the BIOS will not have power-management capabilities installed under Windows 2000. Guess what. To get APM support, you have to reinstall W2K with APM support enabled in the BIOS.I'm not in any ivory tower on Linux, because the ACPI support is so gacky I can't run it on any of my hardware (they've taken the Opera line on standards, i.e. if your BIOS doesn't work with our ACPI it's because your ACPI doesn't follow the standards which, well, doesn't work in the real world) but still. An entire OS reinstall just to switch on APM? What?