Have a Punto in at the moment intermittent non start. When the vehicle doesnt start we get the fuel level warning light flashing & the fuel gauge at 0. Main engine control relay doesnt close & therefore nothing powers up. When the car starts the lcd display in the instrument cluster flashes constantly. Ive digested all the archives on this one but Im stumped. List of what weve tried follows

Vehicle non start , no power to E/C relay, fuel pump, injectors or coils.
Cam shaft & crankshaft sensors good output/waveforms.
Replaced ECU, no difference.
Substituted fuel pump, no difference.
Checked & replaced engine bay earths.
Checked lines from body control to ecm, ok.

Were suspecting the body control unit, has anybody had to replace one before? Does it need coded.

Any ideas, greatfully received.