He tried the inertia switch already.

 

I think it fixed itself but I happened to enter the car through the passenger door to start it for the first time

 

he may have tried the ineta switch, but in my case it was the push on wire connector that was at fault, once I removed it and refitted it , the 4 way flashes stopped and I could start the engine, IF the car wont start and your flashes are going it the inertia system preventing it starting the Clue is in the flashes they come on automatically when it activated

 

I have had this happen with my D1 and D2 and both times the battery was just a little low. They would crank but no start and the flashers kept going. I unhooked the battery charged it for an hour and reinstalled, both started and flashers stopped. Could have been a loose connection but it was one of those two in my instance.