Windows is a tricky beast to manage. Most of the time it sits quietly, doing its thing with no trouble. Then stuff goes wrong, and it's a nightmare figuring out how to fix it. So here is a collection of instructions and fixes that I've used at some point to make my PC behave.
Windows 10 has a slightly annoying habit of randomly waking up from sleep. It's probably caused by your USB mouse, or something that pretends to be a USB mouse. Here's how to make it chill out and go to sleep.