[TomRi]

If you've found that your Hibernate option is missing from Windows Vista,
it might be from running the disk cleanup wizard and removing the hibernate files.
This is due to a known bug in Vista that might not have been hotfixed already

Type cmd into the start menu search box, and use Ctrl+Shift+Enter to open in administrator mode.
You can also right-click the item in the menu and choose Run as Administrator.

From the command prompt, type in the following command:

powercfg /hibernate on

pa restart