My desktop's Windows 7 installation was working perfectly but recently I ran into a problem where it would not come out of sleep. The system seems to be running it's just that it won't come out of the sleep state. If I have to guess I would say that it's not recognizing the USB and thus not waking.
I'd say this was a standard problem with Windows not sleeping/hibernating properly, but it was working fine for about a year and stopped working around two weeks ago.
I have hybrid sleep ON and USB selective suspend ON.