I have both a first gen nexus 7 and a second gen nexus 7 and I can confirm that they DO have a power button.
The second gen nexus 7, made by asus, has the power button on the side near the front facing camera.
I have locked mine many times and what Allnei says works ... most of the time. The only time that did not work for me I just left it sitting unplugged for a week until the battery was flat then charged it back up and it was fine.
hes saying it cant be accessed because of the way BFL integrates it into their miner.
Opening the case may void the warranty.
I would call bfl