I shut it down most days. This time I turned the power supply off itself. That's what I meant.
I've realised which application causes the problem. It's so beyond me to even start figuring out how to remedy this that i think i'll leave it, maybe wait for the update. I might go and post on their forums but then again it could be all down to my system.
(the app is called Steam, by Valve. Gamers will know this is the thing that loads Half-Life and Counterstrike etc.)
So... the problem isn't really solved as I first thought.