Adobe uses Nikon software to connect to the camera and the Nikon software would use the OS's USB drivers, so something not being right in either of these could be a problem outside of Adobe's control.
Do you have any Nikon software installed that might be latched onto the camera?
Does closing Skype fix the problem, in case Skype thinks it is a webcam and grabs it?
I dont have any Nikon software installed. I found a piece of tethering software called digicam control to tether the camera which is just incredible and most importantly....it works.
Jumping in to say I've had *CONSTANT* trouble with Lightroom and the D800, both on Win 7, Win 8, Win 8.1 and Win 10. Versions 5.7, 5.7.1 and CC.
It's never worked consistently, and has often embarrassed me in front of clients. Totally sick of it.
I have started to use digicam control, it works, it has so many more features than what is available in lightroom and it is free. Give it a bash and see how you get on.