Don't take this as the word of an expert, because I'm not, but if it happened to mine I would check the fault codes for pressure regulator faults, (looking for open or short circuits). Then pull the injector return line off the fuel collector tank (on mine it's above the HP pump), plug the tank port, and watch for fuel flowing from the injector return line during cranking. If it does then an injector is leaking, preventing the pump from generating sufficient pressure.
If the 70 Bar reading came from the car's sensor, perhaps it is reading low, and the pressure is actually there (though what stops the pump over pressurising the system in this case I don't know). You could get the sensor checked by an injection specialist, or try another.