My Nexus 7 worked great. Never had a problem with charging or anything else. Now when I updated to Android 4.4 it froze when about 1/3 done. I left it for about 2 hours, still nothing. So i did what i found by searching online and pressed Power with both up and down buttons. Now it doesny boot up. Can anyone help me with this. I tried quite a few things like charging overnight and holding power for 15 seconds. HELP