i had same problem with mine couple weeks ago on my build win 8.1. needed to change usb ports and instal the newest firmware and instal it couple of times. now it work but sometimes it messes up the component layout or some programs wont let the program to turn the fans up.
i really want to hear more arguments about G-Sync versus <144Hz monitors. Today there is even 400 or 1000Hz TV's to buy. if G-Sync is only equivalent to more Hz than whats the point.