Does the low pressure electric fuel pump run for about 5 to 10 seconds when the ignition is turned on? (Ignition Key in MAR position).
Take the cover off from inside the boot if you dont hear the fuel pump running, untill it times out with the key in the MAR position.
Have you (or the Garage) checked the relay connections at the front of the battery, particularly as mentioned the Fuel Pump & Injection Relays!
The Crank Position Sensor (CPS) tends to go open circuit as the engine warms up, with no crank position the ECU stops the engine, and gives the normal display warning MCSF.
But normally restarts when the engine cools (CPS now back in circuit at about 900 ohms @ 60C).