Uhhh I also found this, and it could apply to your situation......
The BIOS upgrade requires and upgrade of the Hardware Abstraction Layer (HAL) of Windows XP. Some HAL upgrades can be accomplished by using the Device Manager, in particular the Device Manager can be used when upgraded a single processor system to a multi-processor system. However, the change from non-ACPI to ACPI by changing drivers is not supported. To properly make this change, an in-place up grade (where the computer is converted to ACPI during Setup) is mandatory. We must reinstall the operating system.
Note: The HAL (Hardware Abstraction Layer) is a set of drivers, upon which the Windows NT kernel is based.
If the installed HAL is incorrect, you may have a problem ranging from certain settings not working (such as
ACPI or APM) to Windows not starting at all.
Reference: HAL Options After Windows XP Setup (Q309283)
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