Yesterday I decided to run the Windows Vista Cleanup tool, which enables you to clear your disk of unnecessary files. Main reason was that I was running out of space on my C:\ partition. So I only selected my C:\ drive to be cleaned up. After selecting the Disk Cleanup tool this dialog pops up:

Selecting the C:\ drive to be cleaned up.

The dialog below shows that the hibernation file cleaner will free up 1,99 GB of space. This is the "hiberfil.sys" file that will be deleted. The description of this file can be read below:

In total I will be able to free up 2,04 GB of space from my C:\ drive.

After having cleanup the files I cannot see the Hibernate option in Power Options anymore.This problem occurs when the Disk Cleanup Tool disables the hibernation file. The hibernation file must be enabled to access the hybrid sleep feature and the hibernation feature in Windows Vista.
When the hibernation file is disabled, and the hybrid sleep feature is enabled, a backup of open programs and open files will not be saved to the disk when you use the sleep feature in Windows Vista. Additionally, if the computer loses power while the Windows is in sleep mode, open programs and open files will not be recovered, and any unsaved work will be lost.

In order to get the Hibernate option back in the Power Options mode you should take following steps:

1. Click Start   Start button , click All Programs, and then click Accessories.

2. Right-click Command Prompt, click Run as administrator, type powercfg -h on, and then press ENTER.

The command line tool powercfg.exe enables users to control the power settings on the system. An overview of all parameters that can be passed to the cool can be found by running the command "C:\Windows\system32>powercfg /?"  from the command prompt.

For the hibernation we need the following:

-HIBERNATE, -H <ON|OFF>
Enables-Disables the hibernate feature. Hibernate timeout is not
supported on all systems.

Usage: POWERCFG -H <ON|OFF>

After running the command above with the hibernation parameter - powercfg -h - the problem is solved and I can again hibernate my Windows Vista system. This applies to all Windows Vista editions. More information can be found in this support article "".