if I remember my encounter with fastboot and Windows 7 machine correctly, W7+ does not allows unsigned drivers, but, unlike XP, which asked you to confirm installation of unsigned drivers, W7 silently skips it. Your fastboot drivers maybe installed but not loaded, until you allow unsigned drivers in W7 as such, via special "testing" reboot. Google "permanently disable driver signature enforcement". or use XP inside Virtualbox. That actually works.