Thank you all for great answers. I had the same issue. Nexus 7 2nd generation almost brand new and fully charged was not turning on. I tried to charge it for an hour then for 10 hours and hold the power button for couple minutes. Nothing helped. I have followed the steps at Nexus 7 2nd Generation Teardown and opened the back cover. Disconnected battery for few minutes and once I put it back together, the tablet booted up with no issues. Once again, the interweb has saved the day.