Nexus 10 not booting, showing Google and lock icon when turned on

This is odd. My Nexus 10 has been working great a quite a while now, but now, suddenly, when I turn it on, its quickly shows a Google title in the middle, and a lock icon at the bottom (in landscape mode only). The lock looks like a padlock and it looks open (not fully closed). Nothing happens when I wait. I can turn the tablet off by holding the power button for about 5 seconds. The tablet then stays off, until I press the power button for about 1 second. "Google" and the open padlock icon then reappears. I've image-googled for anything about not booting and lock icons and whatnot, but I can't find anything that resembles this. I've had an ipod touch years back and after my toddler tried to log in a few times, I lost access to it, and lost all my data. This made me not wanting to try Apple again. I seriously hope I'm not dealing with something like this here now again...