ACPI driver missing and can't update...

My Alienware HD died and it was replaced by DELL and they reinstalled, all is OK except the machine won't wake from standby.  Under devices I see an unknown device, clicking on details its ACPI - power management.  I have tried:

• Uninstalling/deleting the device, rescaning.
• I tried googling for a driver, but I couldn't find an actual driver.
• Windows Update has nothing.
• Browsing the Alienware install disk window says there are no appropriate drivers.

So I am at a loss.  Any advice on how to get the right driver?

Thanks in advance.