I have been following this thread, also trying to figure out why my computer wasn't going to sleep on it's own, and wakes up by itself. After all of the attempts from the first page of this thread, I read you unplugged a joystick and that solved it for you. I recently purchased a Thrustmaster flight control joystick/throttle system for Microsoft Flight Simulator, and after unplugging them, my computer is behaving nicely.
This thread is little over a year old, but solved my issue. So glad you posted this, and that I found it!
Thank you!!