Hy Mearl, did you install a combination valve with your new master cylinder? It sounds like the valve may have shuttled over shutting off flow to the front brakes. If you can generate any pressure in the front brakes, you could slowly open a rear brake bleed screw, this would mean less pressure in the rear system than the front system, and the valve should shuttle towards the center if not all the way to the rear, you may have to chase it back and forth before you get it in the center. Once you think it is in the center close all the bleeders tightly and slowly step on the brake pedal to generate pressure, this should finally center the valve, hope that helps
