After suffering a complete electrical failure which resulted in a loss of communications, the aircraft was landed on runway 11C. The landing gears collapsed during the landing roll and the aircraft settled onto the runway. Subsequent investigation determined that the starter contactor had failed in the start position, isolating the generator. The only available power was then provided by the battery which slowly discharged to the level that radio communications could not be maintained. Although the landing gear selection and locking is dependent on electrical power, there was sufficient power to unlock the gear from the UP position. The gear then extended under its own weight but failed to lock in the DOWN position and consequently collapsed under the landing loads.