F-250 with no power?
 

I have a 1978 F-250 with a 351. I was driving it and it completely shut off. I assumed it was the alternator and replaced it. It started, but the battery had a faulty cell. So, I replaced the battery and it wouldn't charge. Come to find out the first alternator was bad, even though it was new. So, replaced the alternator again, attempted to start the truck, and a puff of smoke came from the starter area. Now nothing will happen when I turn the key. What could the problem be?