Sometimes mine doesn't work either.
I would also suggest disconnecting all other non essential USB devices from your system. You can also remove the Vive USB drivers and try loading them again.
I've see it work in hangouts. So that is stopping me RMA ing for the time being. In the hope they have just not really developed it properly for the variety of systems. Although mine is fairly standard, my mobo is a few years old. I do have a knew PCI USB card that I got for the rift..doesn't work either.