I had a problem recently with Windows 7 refusing to go to sleep. I would click “Sleep” and the screen would go off but all the fans were still going and on moving the mouse around I would be presented with the login screen – not exactly “Sleep” in my books. I was baffled by this and no matter how many times I told the machine to go to sleep it would behave the same way.
Fortunately the cure for this insomnia is relatively simple!