This is an interesting issue. I've never tried using hibernate on a machine with >4gb of ram.
Off the top of my head, I would make sure that you have at least 8gb available on your Windows drive, as the hibernation file is going to be 8gb large.
I would also open up command prompt, and execute this command, "powercfg /hibernate on" (without the quotes). After running it, check to see if you can select hibernate in power options.
Let me know if that helps!
- Ryan Hoffman
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