Just a quick thought before others chip in.
That 'always left on'. Have you rebooted since you noticed this?
I've had the audio go MIA recently on my 5+ year old PC running Windows XP. I opened Device Manager to Sound, Video, etc. and under Creative SB Audigy
it shows the item as "This device is working properly".& Location: PCI Slot 2 (PCI bus 3, device 10, function 0). But in Control Panel under Sound & Audio Devices it shows No item installed and all the controls are set to zero and they no longer are movable. This seems to have happened out of the blue as my PC is always left ON and everything was copacetic an hour or so previous.
My SB Audigy device is no longer supported on the Creative site as far as I can tell. I can't specifically ID my device's serial number from the info in the driver properties.
I did however buy Driver Detective and run that. It showed a download that it felt was proper for my device and after downloading and installing that I am still without sound and all previously described details remain the same.
Has anyone else experienced the loss of integral components with no rhyme or reason? Is there a cure for my situation? Any help would be most appreciated at this point.