Re: What can brick an unrooted Nexus 7?
It's highly unlikely that any applications you installed caused the problem, it's more likely that it just 'happened'. As it has been said in previous replies, these things do just 'happen', on occasion. The good news is that you're unlikely to experience it again (or, at the least, again soon). If you do encounter the problem again, however, it may well be a defect with the device. Hardware problems (charging circuits, main board, etc.) can all cause strange behavior such as what you've described, as well as states similar to the infamous 'sleep of death'. If something goes wrong, reset to stock and get in touch with Google to see what you can arrange. Don't let it shake your confidence in the Nexus 7 per se; technology is (unfortunately) far from perfect.
Originally Posted by Torsten Uhlmann
There's one fact that should bring you some solace and build that confidence back up: having a Nexus device makes it very, very easy to unlock/lock, root/unroot, and back up/reset these devices, as you've already experienced. Fixing any issues with a Nexus device is almost always a simple endeavour in which you learn a bit more about the device along the way.
It looks like you're relatively new to AC as well, so welcome. It's a great place to be