Car won't start

I have a 1995 Cadillac, El Dorado. Had a starter issue, replaced the starter, when I tried to start the car, it went dead, all the lights and the dash instruments worked, but when I turned the key to start, lost all power, and the starter didn't do anything. Had the starter checked, and its fine, had the module checked, and it was bad, replaced it, and again the same thing, car didn't do anything. I charged the battery, and no change, car still won't start, help please, this is our only means of transportation....