Hibernation button is missing in windows vista
The hibernate button disappears after a disk cleanup utility was been used
Or after you delete the hibernate file.
You can return hibernation by running command prompt (CMD)
Right click on the command prompt. Run(CMD) as administrator.
Type the following command:
powercfg /hibernate on
This should return your hibernate button.
Please note if you run CMD not as administrator you will receive error “You do not have permission to enable or disable the Hibernate feature.”