Have you tried to clean the terminals on the battery? My car had no power and would not start, so I took the battery out and had Autozone test it(I couldn't drive it there). It was fine, but that thing was nasty looking! I bought a terminal brush for $1.99 and cleaned the posts before putting it back. I decided to try to start the car before calling to have it towed, and the thing started up with no problem. This may not be your problem, but it's worth a try if you haven't done it already.
