Win 8.1 Machine: Dell XPS 15 (2013 High Res Touchscreen edition). Lightroom 5.7, all windows updates applied. Drivers up to date.
Camera firmware up to date as of Jan 2014. (A, B and L all at latest versions).
The camera shows up in device manager, can be browsed in Windows Explorer. It does not work in Lightroom when tethering, simply states no camera detected.
Nikon Technical say they've tested against their Win 8.0 and 8.1 machines and it works fine. Despite being very friendly and sympathetic, this was about the extent of their help. They confirmed that there are no drivers for the D800 and that the OS should install the generic USB device driver, as it has done so on the Win7 machine.
Camera firmware is up to date, camera batteries are fresh, all tests have been conducted with and without a memory card in the camera. I've used a USB2 Micro cable, a USB3 Micro cable in both USB2 and USB3 sockets, as well as through a powered USB3 Hub and an Active USB3 extension cable.
Tried changing the USB3 routing mode from EHCI to XHCI and that didn't change a damn thing either.
Any input gratefully received, I'm flat out of ideas and very frustrated. This has screwed 2 professional shoots now where we've had to resort to shuttling memory cards to the laptop, my confidence in Lightroom now approximately zero.