This is almost certainly going to be an easy fix, ... I hope. Sounds like the shifter cable became disconnected on one end, or it could have broken. With the transmission still in gear, the neutral safety switch prevents the starter from engaging. The transmission needs to be in "neutral" or "park" for the starter to work.
If you noticed the shift lever was getting harder to move over the past weeks or months, that would point to it fraying and coming apart, so it would have to be replaced. That isn't terribly common. Most of these cables are just snapped on so they go together faster on the assembly line, but that makes them pop apart easier too.
To get the engine started you can have a helper bypass the starter relay under the hood after you turn on the ignition switch. Remember it's still in "drive" so keep your foot on the brakes. You won't be able to back up, and once you stop the engine, it won't start again with the ignition switch. If you need to back up, your helper will have to crawl underneath to move the shift lever to "reverse" by hand. That can be pretty dangerous. If you like that person, be sure to keep the brakes on. I had to do that once with my parent's relatively new car. Once they backed out of the driveway, I crawled under there again to shift it into "drive", then later I manufactured a much better design to prevent that linkage from popping off again.
Wednesday, October 9th, 2013 AT 1:06 AM