Laptop Won't Hibernate Anymore?

I noticed a (very long) thread that is exploring issues with Windows 8.1 not sleeping properly, and while I've also had issues putting my computer to sleep, I'm more concerned right now with its inability to hibernate. I've been having my laptop hibernate most nights since I got it last year, and it's been working fine (with the occasional shut down instead of hibernation) up until a few days ago. It will not hibernate anymore. I have every power option set to 'hibernate': it's supposed to go into hibernation automatically when I close the lid, push the power button, anything. I've also set up a shortcut on my desktop that used to put it into hibernation, but now, when I go to wake it up afterwards, I've found its has shut down and closed all my apps and documents. At first I thought I was waiting too long between sessions and it automatically shut down after 12 hours for example, as I've recently come home from college and I'm going longer between wake-ups, but last night I put it into 'hibernate' and an hour later tried waking it up only to find it had had shut down again.

I've got Windows 8.1 but hibernate was working for weeks on it until recently. I've DEFINITELY got hibernate enabled in my power options, I've checked about a million times. I don't think I installed or changed anything around the time I started having these issues.