In Windows 8, Power controls are located in 'Control Panel'. Go to Power Options in control panel. Then follow the below mentioned steps.
1. Click on 'Choose what the power buttons do' hyperlink in the left side section.
2. In the next page, click on 'Change settings that are currently unavailable'.
3. Then scroll down to the bottom and find 'Power Options settings' section.
4. Now check the box next to 'Show Hibernate' option to enable it as it is disabled by default.
5. Click the 'Save Changes' button.
Now you can see the 'Hibernate' option in the Power Off Section.
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