Hibernate

cant find hibernate - laptop used to have hibernate function when i went into shut down options, now it doesnt have it. how can i make my laptop hibernate again? its vista I have the same prob. The hibernate option does not exist anymore. I tried the solution offered, but after typing powercfg/hibernate on at the prompt, I get a response that I do not have permission to enable or disable te hibernate option, and I am logged on as administrator, and I'm the only user. I am running Vista home premium.