If logitech software is installed, uninstall it. Or at least kill the running process. This has been a know issue reported in this forum before.
Try a different USB port. Some USB 3.0 ports do not accurately detect some USB 2.0 devices. This has also been a known issue reported in this forum.
Try a different USB cable (perhaps borrowed from a digital camera). I have purchased (low quality) mini-USB cables at the dollar store. Using a different cable was reported to solve the problem for some people, when the earlier suggestions did not work.
If all else fails, test your Rift on a different computer. The video does not need to be connected for the Head tracker to work.