signal problems - DirecTV DVR

For signal problems, relating to DirecTV DVRs and receivers. last week i lost all even transponders. i have a phase III triple lnb, with three cables going to two receivers. The problem was the same on all cables, and receivers, regardless of configurations. i had an extra used lnb and installed it. The system worked for a day and then, i only had signal on satellite a. Now i have no signal, anywhere. i know the dish is pointed correctly. Any help would be greatly appreciated