I had the same issue, I recommend just flashing the full images now that they are posted to the google site:
https://developers.google.com/android/nexus/images
If that is not an option, have the phone in recovery mode (the yellow text with black background) plugged into the computer with the "Device Manager" screen open on your windows computer. I kept on losing ADB at this point until I unplugged the usb cord on the side that plugs into the computer and plugged it back in again, at that time windows made a PNP sound then I refreshed the device manager screen and the unknown android device popped up. At this point, click into the unknown device, then update the driver and choose something like "browse my computer for existing driver" or whatever it is, from the list, select the koosh driver and you should be good to commence the sideload.