Well I don't know but my book on XP says...
"...you should disable all power management features in your computer's BIOS. Run its set up program (Del or F1 during power up) and browse the menus for all settings related to power management. Power management should be under the exclusive control of the operating system. When theOS and the BIOS contend for control problems often result."
It also says...
"Power management features - in particular standby & hibernation - rely on device drivers that support power management in addition to additional hardware. In particular, incompatible video drivers prevent these features from working. The built in VGA driver for example is a bare bones driver that doesn't support power management. If standby & hibernate don't work, install an updated driver for your display driver."
Good luck...
P, June 2009