Nexus 7 stuck at Google logo, and system recovery, and OEM locked
This sounds like a common bug that has been reported on recently by Android Police. To summarize:


  Affected units stop booting at the "Google" logo screen.   Attempts to
  unlock the device through fastboot fail at the "erasing userdata..."
  step, leaving the devices locked.  Some users report successfully
  flashing factory images on unlocked devices, but this still doesn't
  fix the problem.  There are mixed reports about starting up in
  Recovery, with some users complaining that the Nexus 7 freezes, and
  others being able to get in to perform some maintenance.


There are no know solutions at this time. Sorry to bring bad news. I hope I'm not right.