If you want to enable hibernation on your machine running on Windows 7 you need to run following command:
powercfg -h on
You can verify whether the above command was successfull or not by checking start menu. Hibernation option should be visible now.
If the above method didn't work for you try tyhe next method:
Click "Change advance power settings" in Control Panel.Navigate to "Sleep" option.Select "Off" to "Allow hybrid sleep" option.