1998 Lincoln Continental Occasionally starts

My car just started not starting when the key is turned on. When I insert the key in the ignition and the driver's door is open, the bell will ding and the car will start. But every time I insert the key and the belll doesn't ding, the car will not crank or do anything. I've checked the battery and it shows fine. Sometimes I can shift through the gears a few times and the bell will start dinging and the car will crank. We can not get the diagnotics machine to pick up any code errors.