My car is shutting off

Hello.I have mitsubishi galant 3.0 2003
Two days ago i drove the car and I turned it of .After 20 minutes I couldnt start it.All lights came on but not starter,Even any sounds.Next day in the morning I tried,It started first time and drove two three miles.
When i was parking it my steering while became hard and i saw motor shut off too.It started good and while driving again engine shut off.I called towing truck and brought to mechanic shop.They checked it two hours and even they drove some miles but they dont find anything it seems that it never happened.Now I dont want to stop in the center of highway again.Please I need some advices.

does it only happen after it gets hot? could be a faulty crank sensor.