If the Advanced Configuration and Power Interface (ACPI) option is
enabled in your computer's BIOS when you initially install Windows 2000
and you later disable the ACPI option in your computer's BIOS, you
receive the following error message on a blue screen when you start
If you want to disable ACPI support after Windows 2000 is installed, you
must reinstall Windows 2000 with APCI disabled in the computer's BIOS.
Because numerous changes are made to the registry and system files, an
upgrade installation does not work.