Lordlee,
Install Recovery Console. Then manually set the HAL back to MPS Multiprocessor PC.
OR
Boot from the Cd and do an UPGRADE.
It is a no-no to try to go Std to ACPI. The standard MPS install omits all of the ACPI support such as IRQ Steering stuff. MS has numerous KB papers on this subject.
In point of fact, enabling ACPI doesn't really buy you anything except just that, advanced power management. So what?? If you've a desktop box are you all that concerned over a few watts of AC Mains power??
ACPI certainly does not provide any speed or other performance advantage.
BFN
WCR