Our car won't start and no one seems to know why?

I have a 2011 Ford Galaxy and it has just stopped starting. It is currently sitting at our local Ford garage who have run two diagnostic tests - one mechanical and one electrical test - and have come up....

My car won't start - can you help me?

My car has problems starting. A mechanic replaced the straight front exhaust pipe and after a couple of weeks the car doesn't start. The mechanic tells me the filter and catalytic convertor are sooted...