Starter problems

Boyfriend stopped at bank, cut car off, and it would't restart. He replaced the starter and still wouldn't start. Someone noticed that the break lights where on and told him that the starter was part of a three piece mechanisim. Replaced some mechanisim under the breaks, wouldn't start, now they say the only thing left is in the shifter.
What is the deal? It's getting power, all the lights and everything are on, it is just not turnning over. What else could it be?