My Wife's Zetec Blue with the Sony system has done the same thing 3 or 4 times.
This car is used daily for our commute to the station and for the Tesco trips.
Try opening the passenger door or turning the ignition on/off/on before starting the engine - either has brought the Sony to life, not ideal but I thought that taking it back to Ford would just cause grief - you have just confirmed my fears.
Would appreciate it if you could post the fix to the problem - best of luck!
i have had the zetec blue for a month with no problem so far. will keep an eye on it though.