I have a Google Nexus 7 and the tablet did not start today. When I had it plugged in, the screen would be on, but it would be black. Then, I would see it flicker while it was still black. When I unplugged it, the screen would go off. In fact, the Nexus 7 did not turn on at all when it was unplugged. I tried holding the power button, but I was always stuck with either a black screen or a black screen that was flickering.
So, I decided to pull the back off the Nexus 7. Then, I saw the problem: it was a loose battery connector. In fact, the battery has some wiggle room and it must have pulled the connector loose. I inserted the battery connector, and the Nexus 7 started up without any problems.
If you have a Nexus 7 that isn't starting up or is stuck on a black screen, maybe the battery connector is loose. The back comes off fairly easily. Take a quick look before you send it in for warranty support from Asus.