You have probably adjusted something, though Microsoft are very good at undoing anything you do to disable automatic updates. The update system by default wakes the PC up in the middle of the night to reboot it. In my experience it more reliably wakes the PC up than rebooting it, so what happens is you just have a PC which turns on in the middle of the night and sits there idling, which is extremely irritating if you happen to sleep in the same room, and accomplishes nothing.