hmm - I seem to have the same problem.
I just changed my processor from FX-55 (single core) to Opteron 170
(dual core). All other components remain the same.
When I check Device Manager, under Processors, there are 2 listed.
Under Computer, I have ACPI PC.
When following your recommendation and trying to update the driver, I do not have the option ACPI Multiprocessor PC available. The only options available are the one currently installed, and Standard PC.
As the other poster, CPU-Z does not show 2 cores, and neither does Task Manager.
Are there any other solutions to this problem, or will I need to reinstall WinXP ?
Thx in advance
System:
Coolermaster Stacker
Tagan TG580-U15 580W 'Easycon
ASUS A8N32-SLi Deluxe BIOS 1103
Opeteron 170 (no OC yet)
Zalman CNPS9500 heatsink
2x1GB Corsair TwinX 3500LL Pro
XFX 7800 GTX Extreme XXX (490MHz/1.3GHz)
X-Fi ExtremeMusic
4xWD740 'Raptor'
Plextor PX-716A DVD-RW
Logitech Z-5450 5:1 speakers
WinXP Pro SP2