Are you using hibernate or sleep?
Hibernate records the contents of ram to a file and turns off the pc.
That is best for power savings.
Sleep is similar, but the contents of ram stay active, maintained by a low amount of power and the monitor enters a low power mode.
Sleep/wake is faster and a good option if you never leave anything important in ram.
I think windows can wake itself up and do some updates; I could be wrong on that.
Unless you have set up in the bios to disable a usb connected device do the resume, you could have cats walking over the keyboard causing the wake up.