ignition coil exploded

i was working on my car tonight after it was sitting all winter, and i put new plugs and wires on it. i was trying to start it but it wasnt getting spark. the coil was getting sort of hot, but i didnt think anything of it. and then it exploded all over my paint. what could have caused this? distributor wasnt getting spark, and the coil was obviously getting juice. anyone have any idea ? oh and by the way, i have no ballast resistor , its a 440 source distributor with the box built in. so i just want to get this all figured out.