The pilot was conducting solo circuit training and had completed 8 normal landings with no problems. He reported that the weather conditions were fine with no noticable crosswind component on the runway in use. He stated that the last approach was normal, but as he flared for landing the aircraft continued descending and touched down hard and bounced. He attempted to raise the nose to cushion the landing, but there was no response from his elevator inputs. The aircraft again contacted the ground heavily in a nose low attitude, shearing the nose landing gear attachment frame from the forward fuselage bulkhead, pushing it upwards and shattering the windscreen. Both propellers suffered ground strikes bending the blades. The pilot may have reduced engine power too soon prior to the landing flare, resulting in a reduction of propeller slipstream over the tailplane, with a subsequent loss of some elevator authority.