I had the exact same problem. Can you verify that you're unlocked? In the bootloader it should say: Lock state: unlocked (or something similar). Also, when you boot up, the black Google screen will show a lock symbol at the bottom of the screen if you've successfully unlocked.
Once you know you're unlocked, power your phone off and connect to your computer. Three finger salute into recovery. Re-run the Superboot file (more specificaly: install-superboot-windows.bat) by double clicking on it in the root folder on your C-drive. It should boot to the black Google screen. Give it time. If it hangs, just wait 5 minutes, then pull the battery and reboot.
When I double click on the install-superboot-windows. bat file in the c:/root/ folder, I get the blue bar message at the bottom of the fastboot screen : FASTBOOT STATUS - download:00467800" and that is all the happens. No Google screen, no other change. I am unlocked according to the "LOCK STATE: line on the Fastboot screen. Thoughts?