The helicopter made a hard autorotative landing after a power loss. The pilot stated he was hovering about 75 ft AGL waiting for ground personnel to attach a line to his external sling load when the engine decelerated to flight idle and he could not regain power. He initiated an autorotation but the RPM had decayed and a hard landing resulted. After the accident, the pilot said he found the PY accumulator from the engine governor laying on the ground a short distance from the helicopter. After the accident, before finding the accumulator, the pilot had started the engine. He stated it ran okay but would not accelerate above 30 percent. Investigation revealed that the Allison 250 turbine will operate at only about 30 percent of its rated RPM without the PY accumulator. The pilot thought the accumulator should be safety attached to preclude separation from vibration. The pilot said that the subject parts had been reinstalled on his helicopter after removal for maintenance only 2 and one half hours prior to the crash.