Auto Parts: car problem, corrosion, cables

Question
my car wouldnt start, the next day i took out the starter and tested it. it was fine, i put it back in and my car turned on, what could of been the problem?

Answer
    Since all you did was remove and replace the starter, I would guess that the cables to the starter were loose or corroded.  When you reattached them, it knocked the corrosion loose.  You should inspect both ends of each cable and clean them if you see any kind of white or green corrosion on them.