I have a hard bricked nexus 7,
did you try to get an image for your nexus device from this place: https://developers.google.com/android/nexus/images?hl=en and flash it ? If nothing is wrong with the hardware then this will help, just follow the steps provided on that page. 

By the way, i've upgraded my nexus 7 to the latest Android 5.1.1 and i could not use it, because it keeps on freezing, rebooting. Had to downgrade back to 4.4.4 and now my device is back.