1984 Cadillac Sedan De Ville will turn over but won't start what should i do?

If by nothing you mean it acks as though there is no battery in the car try this it worked on my (1990 DEVILLE ). Put the car in park ,Attach a remote starter switch to the starter,remove the air cleaner,turn the key to the on position, put approx one teaspoon of gas in the intake manifoil throat and try to start the engin using the remote starter. If the car starts the problem is somewhere in the pass key decoder circuit which includes the starter enable relay ,the fuel pump relay,key warning ,seat belt warning ETC. Your car has on onboard diagnostic computer which will give basic problem codes you can find out what the codes mean in a Haynes Repair Manual for your car. I repaired my car by bypassing the starter enable relay and the car works fine (but if the battery is disconnected for any reason I must charge the engine with a teaspoon of gas to restart the car GOOD LUCK a repair is $600+