A friend of mine owns a 2002 Toyota Corolla with around 100k miles on it and it has some sporadic problems. Once in a blue moon the engine light comes on because of a misfire and seems to be around the same time it is humid and wet out (suggesting spark plug wires). However it recently sat overnight, after a slow rain, and would not even turn over the next day. The lights are not dimmed in the car but there is only a faint hum when the key is turned. What is wrong? Any ideas would be greatly appreciated.
The short list that comes to mind instantly: Neutral safety switch, starter relay,loose or corroded battery cables at the battery and starter. Probably a few other things, but those are the most common.
If it is the neutral safety switch, try shifting to neutral and see if it starts.