did your mechanic check your battery cables for corrosion when he replaced the battery? I had to cut away about 4 inches of my negative cable and replace the connecter. it had managed to get corrosion inside the the rubber/plastic casing on the cable. Mine had sat a couple weeks and then wouldnt start, replaced the battery and still nothing. fixing the corrosion and connecters did the trick, fires right up now. just something to consider