Car not starting unless I move gear shifter. Bad sensor?

What is your question?

So replaced my battery and alternator last month, my car started not starting, wouldn't click or try and turn over and couldn't be jumped. Mechanic couldn't find anything wrong as it started just fine for him. Drove it today and as its been happening for about a month now. My car would not start. Called the mechanic. He suggested I move the gear shift, I did. It started right up. However now every time I try to start my car I have to move the gear shift.