Prior to my retirement, I was a Field Service Engineer in electronics....telemetry systems and computers...all of my working life. That aside, the worst problems to isolate are caused by poor grounds, poor power source and corrision issues on contacts. About the only thing you can try at this point is cleaning your battery and lens contacts and trying a different lens. I certainly wouldn't reccomend that you go internal to the camera. Too many things to really foul up if you dont have the experience. It is very chancy, even with videos. I hate to say it, but if cleaning contacts doesn't help, you are probably looking at sending the D700 to Nikon or an authorized repair center (with the lens so they can recreate and verify the problem). Is your 5 year Nikon warranty still valid?