Just had exactly the same thing happen to us in our 147 GTA project. Car was driving absolutely perfectly about a week ago and when we tried to start it up yesterday it idled for about 20 seconds and then just completely shut off suddenly. Immobilizer and VDC errors on the dash when we turn the ignition now.
Hoping its the loose capacitor issue everyone seems to be having, otherwise we have no idea what to do after that since there's no second hand ECUs or new ECUs anymore.
Maybe you can check for the same thing with your ECU? I'm going to open mine up and report back later.