Help! My SB-600 speed light will not flash. It has been sitting in my camera bag unused for the last 3-months. --I've installed new batteries --battery terminals appear to be clean and uncorroded --ready light comes on --i've double checked to make sure batteries were installed in proper position --It goes to STBY mode ok. --It does not fire when I try to do a test flash..not does it work when I put it in my D7000 hot shoe. ANY THOUGHTS?