For Windows XP, you have to go to device manager and uninstall the CPU and/or the motherboard, that will reset them to generic ACPI something if I recall well.

For Windows XP, you have to go to device manager and uninstall the CPU and/or the motherboard, that will reset them to generic ACPI something if I recall well. I've done it once, migrating a very old machine to new hardware by just moving the disk.