I have a similar problem with needing to do a factory reset but can't access any menu.
Managed to root my Nexus 7 and now trying to unroot it. Stuck on the black screen with the green start block upper right and the unlocked lock at the bottom. When I select "start" nothing happens, when I arrow down with the vol button to "restart bootloader" and select that is comes back to the screen with the android lying on his back and the start box again. When i select "Recovery mode" i get a tiny message in the upper left corner that says "booting failed". I have tried every combination of buttons available. Can't get to any menu screen at all. When I connect it to my computer it does not recognize the device and cannot find any drivers for it. Tried everything in this thread. Is my Nexus beyond repair?????? Help........please...:'(