My PC hates hibernating, in fact, it hibernates for a whopping minute then wakes up due to the genius default driver power management settings.
A quick way to find the culprit.
Open command prompt and ask...
C:\Users\Chris>powercfg -lastwake Wake History Count - 1 Wake History  Wake Source Count - 0
Of course, if it had woke up it would tell you what caused it.
My network card had reset its settings during some update and had decided it should wake my pc up; machine shuts down, router says hey where did you go, machine powers back up.
One check-box and bang, fixed.