1981 Buick Century 1982 Limited 6 Cyl 3 8l Changed Out Spark Plugs Ignition Coil

i have a 1982 buick century limited 6 cyl 3.8l and i have changed out the spark plugs and ignition coil and cleaned the0 carberator and the car cranks over but will not start. what could it be? about a month ago i got it started with starting fluid and it stayed on but now it wont even start with that. oh and i put half a tank of new gas in it.