|Intermittent power fluctuations might also "wake-up" your machine. These can be coming from the mains power supply (in which case an electrician will be needed) or could be a symptom of a faulty PC power supply (it can be tested and replaced if required).|
Most likely Ed is right about the cause. Virus/malware removal often leaves traces behind that can be troublesome. It wouldn't hurt to clean up the registry to remove entries placed there by nasties.
Check also that no background programs (that use the system timer for one or more functions) are interfering with the hibernation cycle. Examples might include the use of animated graphics (flashing lights, etc) on a programs interface, or perhaps a time-out or error-correction subroutine. Too often people have programs running in the background, even when they are seldom used. I regard that as a senseless waste of system resources. Try stopping all background programs (maybe one at a time if you want to know which is the cause), before hibernating the machine.
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