Hi. Was having same issue with Nexus 7 not starting, and read all the above.
Best advice: open the N7 and re-connect the battery. I opened mine with my thumbnail, pushing in where the back case meets the metal frame, then moving my thumbnail down the sides till the back popped off. Pried up the battery with a paperclip (easy to do) and found its plug to be just barely making contact with the socket. The battery can move laterally and this causes the plug to come out if its socket. Stuck a piece of cardboard adjacent to the battery to prevent it from moving laterally (and unplugging itself). Putting everything back together, the N7 is now charging properly and working fine!