Not sure what else to suggest, are you running CMD as administrator?
When you boot into the bootloader and start fastboot, does it say FASTBOOT USB in a red bar under the radio and dsp info when it's connected and you are still getting nothing when you type "fastboot devices"?
I found it! When it's in Fastboot, the driver in Device Manager was saying Android 1.0. I updated the driver at THAT point and now everything is working according to your instructions! :icon_ banana: