My PC hates hibernating, in fact it hibernates for a whopping minute then wakes up due to the genius default driver power management settings.
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.