The pilot attempted to hand-prop the airplane's engine without success. He turned off the magneto switch and advanced the throttle to between ½ to ¾ travel and then turned the propeller backwards 5-6 times to clear the cylinders. The pilot reported that he returned to the cockpit and turned the magneto switch back to the on position but did not put the throttle back to idle. He hand-propped the airplane a second time and the engine started. The engine's throttle setting allowed the airplane to move forward over the wheel chocks, and the airplane struck the pilot. A passenger was still in the airplane as it collided with a hangar, resulting in substantial damage to the airplane's firewall and fuselage. The pilot was seriously injured, and the passenger was not injured.