On January 11, 2004, at 1410 eastern standard time, an Aero Commander 500, N800SL, registered to and operated by an airline transport pilot, collided with a ditch during an attempted takeoff at Allendale County Airport, Allendale, South Carolina. The personal flight was operated under the provision of Title 14 CFR Part 91 with no flight plan filed. Visual meteorological conditions prevailed at the time of the accident. The pilot and passenger were uninjured and the airplane sustained substantial damage. The flight was originating from Allendale County Airport, Allendale, South Carolina, on January 11, 2004 at 1400. According to the pilot, while on takeoff roll the airplane began to "track right", differential braking input was applied to line up the airplane with the runway center line. The pilot noticed that the brake pedal felt "soft" and aborted the takeoff. When brakes were applied to stop the airplane, they failed and the airplane veered off the left side of the runway into a ditch. Examination of the airplane revealed the outboard right wing was bent aft and curled upwards. The fuselage was buckled in the wing root area of left and right wing. No mechanical or flight control problems were reported by the pilot. Examination of the wheel brakes revealed that the hydraulic pucks were leaking, and the brake disc and linings were worn. Examination of the accumulator revealed the diaphragm was ruptured and the system would not maintain pressure.