I had the same thing happen yesterday with my Nexus 7 - unable to charge at all - left for a movie with it plugged in and came back to find it had charged for a little while and then back to not being able to charge again. I wonder if the 2012 Nexus 7 couldn't handle the new upgrade - it...
Thanks for your advice. I reinstalled Star Wars Angry Birds because I hadn't started playing yet and had nothing to lose and still black screen. I cleared the cache on it in settings and still black screen so I guess there is something else wrong.