I'm calling your bluff, I want to see a picture of your task manager, there is no way in **** your pc CANNOT be doing anything at all!
Heck. even when the cpu is on total standy, it still has to take requests, permissions and directions from any OS , especially windows.
When the OS wants it's daily checkup for updates or virus definentions for microsoft security essentials or windows defender it will make a little noise letting you know it's working.