My Nexus 7 is stuck in safe mode. I have tried just about everything from restarting, resetting everything, which wiped all of my apps. I've held the power button for 30 seconds and it just takes me to the screen to start, power off, rebootloader, recover with the system info. on the bottom left corner, which says the tablet is "locked." Could that be it and, if so, how do I unlock it?