http://support.microsoft.com/kb/920730
To make hibernation available, follow these steps:1.Click Start, and then type cmd in the Start Search box.
2.In the search results list, right-click Command Prompt, and then click Run as Administrator.
3.When you are prompted by User Account Control, click Continue.
4.At the command prompt, type powercfg.exe /hibernate on, and then press ENTER.
5.Type exit and then press ENTER to close the Command Prompt window.
