Problem with this is your GPS better be pretty accurate. Mine fluctuates and most do and are only accurate with in 5 meters. That is 15 feet.
Also if in your drive way when you start up you will have to have some type of timer that would shut it down after you arrive to keep it from shutting you down when you first get going.
You could use a WIFI signal. When you connect to the internet you can create a script that will look for a specific file that would be located on your network. When it finds it it shuts down the PC.