Shut down be prevented in Windows 2000?

Hi,All

I have a PCI video capture card.And I found a issue when it works in Windows 2000.
When the card works,I press the power button to shut down the machine,but the system pop-up a warning “device driver is preventing the machine to go to the sleep mode…”,just like I clicked “sleep” from the “start” menu,and the system still works.

But when the card works in Windows XP,I press the power button to shut down the machine,it can realized.
A strange thing is:in Windows 2000,when I cliked “shut down” from the “start” menu,it also can realized.

[Summarize]
It can not realize shut down the maching by press the power button when our card works in Windows 2000 even if I delete the function PoRegisterSystemState() in IRP_MJ_CREATE Routine.

Is the issue relevant to the ACPI in Windows 2000?
How can I realize shut down the maching by press the power button when our card works in Windows 2000?

Any help is appreciated.Thanks.

Best Regards
Zhou ChengJun