I would imagine that on most boards the drive would be powered on when the power supply was active. Disabling the drive in device manager just stops the device driver, which could conceivably remove power from the actual physical device, although it would seem an unnecessary expense in the design of the motherboard to do that on most occasions. It ought however, as you said, stop any possible weird software interactions. It does sound like odd behaviour, it's probably just very dirty, or the laser's died. If you've got some compressed air, that may clean the drive enough to make it reliable again, or as said already, replacement optical drives are dead cheap these days. If you were near South Ken I could probably give you one, I've got a pile of old CD/DVD drives from when I replaced them all with CD/DVD-Writers in a load of our old PCs.