At about 17:30 Pacific time, a Piper PA-24-250 was damaged in a wheels-up landing on runway 26 at Chino. The pilot was not injured. The pilot told investigators he initiated a go-around on his first attempted landing because the runway wasnt clear. He forgot that he raised his landing gear. He was wearing a new noise-attenuating headset that changed the sounds he normally heard when flying his airplane. He did not recognize the gear warning horn during the accident landing. He recalled that the gear warning horn was still sounding as he removed his headset.