If by accident or for whatever other reason, the hibernation option in your shutdown has disappered in vista, then this is how to get it back!
- Click on the Start Button
- In the ‘Start Search’ area, type CMD
- cmd link should appear on the top of the list.
- Right click the link & select ‘Run as administrator’
You should see the old black command prompt box with cursor blinking in front of the following
C:\Windows\system32>
Just type in the following command & press enter.
powercfg -H ON
If no error occurs, then type in this next command & press enter to exit the CMD
exit
This should resolve the issue.

Thank you! This issue was such a bugger!
Harris
May 3rd, 2009
thanx i had this option missing n successfully back now
zeb
May 21st, 2009
if u dont want your hibernation icon to disappear then simply dnt tick the hibernation file cleaner box when u r cleaning up uor drive C. (disk Cleanup)
Zain Chawla
August 14th, 2009