To hibernate your PC, first you have to enable hibernation. Right-click on your desktop and click on properties to get to display properties. Click on Screen Saver and then on Power near the bottom...
Then there might be a piece of hardware that is allowed to wake the computer. This can be changed by looking through your Device Manager and seeing what one does and see if its the culprit.
Hibernate is designed as a temporary low-power mode. Whilst it wont actually harm your pc to leave it in hibernate mode for long periods, it's still using power - so - from an environmental...