Nexus 7: Unable to install factory image, stuck in
Well, the device is detected in ADB only, you probably haven't installed fastboot drivers. &lt; waiting for any device &gt; means that the computer is waiting for a device in fastboot mode. 

Download the drivers from this page then install. fastboot oem unlock should work now.

Learn the difference between these two protocols (ADB and Fastboot).

This question may also help.