|If your computer is NOT a laptop/notebook then you can stop Hibernate.|
Hibernation, reserves disk space equal to your RAM.
If it is a laptop/notebook.
Standby & Hibernate Issues in Windows XP
So you've lost (or never had) Standby and/or Hibernate?
First thing: Using both BIOS-based power management and Windows-based power management rarely works. If you are using both, disable one or the other.