The pilot reported that the radio microphone failed as he approached Sandstone. Then the landing gear motor stopped working and the gear only extended about half way when he lowered it on downwind. There was no response from the gear when the selector was subsequently moved to either the up or the down position. The pilot attempted to extend the gear using the alternate system however, the system pressure fell to zero after two or three cycles of the hand pump. He operated the pump for several more minutes without any appreciable result. At no stage did the gear lights indicate the gear was down. As the radio was inoperative, the pilot decided to land at Sandstone rather then return to Kalgoorlie. He observed that, although the main landing gear was down, it was not as far forward as it usually was when locked. On touchdown, the main wheels were dragged backwards and the aircraft slid to a stop on its lower fuselage. No gear faults were identified during the post-accident inspection or at the time of the repair. The system has worked normally since the accident.