Right click a blank space on desktop> properties>Screen Saver tab and
click the Power button under Monitor power. Go to the
APM tab and select "Enable Advanced Power Management support."
If is no such tab there ,then right click My Compute>
Properties> Hardware tab and click the Device Manager button under
Device Manager>select the View menu, and turn on show hidden devices.
In the device manager window, you will now see an entry for NT
Apm/Legacy Support.In the device usage drop down list, select Use this
device [enable]. Hit the OK button and then close the device manger
Restart the machine.
More information here:-
http://www.aumha.org/a/shtdwnxp.htm
regards,
ssg MS-MVP