How to Bring Back the Hibernation Feature in Windows Vista
If your PC is unable to go into hibernation mode, don't worry. You can easily bring back the hibernation feature in Windows Vista (as long as you have an administrator's account).The hibernation feature was probably turned off on the computer because it was running low on memory or because it is a computer that stays on all the time. However, the hibernation mode is a handy feature to have available because it can preserve your files exactly as you leave them, like sleep mode but without using up battery life.
Many people accidentally turn off the hibernation feature. If you performed a Disk Cleanup and placed a check in the Hibernation File Cleaner box to free up space, you not only freed up space — you turned off the feature entirely.
Choose Start→All Programs→Accessories. Right-click Command Prompt and choose Run as Administrator.
Click Continue through the User Account Control warning.
Type powercfg -h on and press Enter.
Close the Command Prompt window.
Vista doesn’t give you any confirmation that the command “took,” but your system will now be able to hibernate and you should have a new, hidden system file called c:\hiberfil.sys.
Click Start. Then click the Shut Down arrow to see that Hibernate is back on the list of options.