Why hibernate option is not available

The hybrid sleep feature and the hibernation feature in Windows Vista may become unavailable after you use the Disk Cleanup Tool
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SYMPTOMS
After you use the Disk Cleanup Tool in Windows Vista, you may experience the following symptoms:
• You cannot see the Hibernate option in Power Options.
• When you use the sleep feature, the computer does not recover its settings if power is lost.


CAUSE
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.


RESOLUTION
To resolve this problem in Windows Vista, run the powercfg -h on command at a command prompt to enable the hibernate feature and the hybrid sleep feature. To run this command, follow these steps:
1. Click Start Start button , click All Programs, and then click Accessories.
2. Right-click Command Prompt, and then click Run as administrator. User Account Control permission If you are prompted for an administrator password or for confirmation, type the password, or click Continue.
3. Type powercfg -h on, and then press ENTER.