On my K70 in Windows 7 Pro, I would have the onscreen display of volume level (let's say it was manually set at 68% using the taskbar icon) when I rolled the dial or hit the mute, but nothing was actually affected on the PC.
Starting the service fixed my problem as soon as I started the service. I think I may have disabled it trying to diagnose the volume control on an old Microsoft keyboard.
Thanks! This post should be stickied.