Seems to be a common problem this month, we have exactly the same problem, drove it, stopped on Christmas day for 5 mins (on a slight uphil if that makes a difference) got back in and it wouldn't start.
Engine management light doesn't show, computer doesn't show an error, it cranks OK, fuel gets to the injectors but the injectors don't trigger.
Suspicion is something in the electronics (ecu or a sensor) but without replacing everything in in turn until we find the answer we don't know how to solve it.
Might a Fiat dealer have further diagnostic equipment or will they be stumped as well as the engine management light doesn't show?
If you work out the solution I'd love to know and I'll let you know if we work it out first!
healeyowners at dsl dot pipex dot com