MG Car Repair: Brakes, brake warning light, shuttle valve

Question
I have a MGB made in Dec. 1977 shipped to the U.S.A. in 1978.  I changed my front brake pads and all was good for about a month.  Now, I have no brakes.  I cannot pump them up.  I tried bleeding them with a "one man" system.  No fluid would come out of them.  I tried both rear brakes and the right front.  I do not think that the bleeding screws are plugged.  Where would be a good place to start to find the trouble.  Thank You in advance.

Answer
Hi Jim.  I need more information.

1) Does the brake warning light come on?

2) Do any of your brakes work or have they all failed?  a December 1977 MGB should have 3 separate pipes, one to each of the front callipers, and a third supply shared by the rear brakes.  In particular, have you lost both front brakes but the back ones still work?  If so, the fault probably lies with the shuttle valve inside the master cylinder.

3) What happens when you hit the brake pedal?  Does it depress normally, does it feel rock hard, or does it hit the floor?