On August 15, 1999, at 1200 central daylight time, a Beech G35, N4473D, collided with the ground during an attempted forced landing eight miles southwest of Columbus, Mississippi. The instructional flight was operated by the pilot under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The airplane was substantially damaged. The certified flight instructor, and the private pilot were not injured. The local flight departed Lowndes County Airport in Columbus, Mississippi, at 1130. The pilot reported that he had recently purchased the airplane and the purpose of the flight was instructional. He further stated that he had completed a preflight inspection of the airplane and it had been topped-off with aviation fuel. During the engine run-up all systems reportedly operated normally, and no obvious engine problems were noted. According to the pilot, the flight departed Columbus and they flew to an upper air training area. Approximately 30 minutes into the flight, the pilot report that while practicing the stall series, the engine lost power. After attempts to regain full engine power, the flight instructor took control of the airplane and established an emergency descent for a forced landing. The flight instructor selected a nearby cornfield for an emergency landing. During the landing phase of the emergency, the airplane sustained substantial damage. During the post-accident examination of the airplane, a substantial amount of fuel was observed in the fuel system. The examination also disclosed that there was no fuel present in the fuel flow divider. The engine examination failed to disclose a mechanical problem with the engine. However, the examination of the airplane revealed that a lawn mower battery was installed in the airplane. According to the pilot an annual inspection had been completed by the previous owner several days before the purchase.