new Cadillac ignition won't Crank car with new key?

[B good]

i bought a new ignition for my Cadillac sedandeville 91 the new key will turn but wont crank the car but the old key will after i turn with new key to get it from the locked position. what do i need to do the new key do not have the ball at the top of the key like the old key does. i no that my problem how do i fix without spending alot of money