Unable to start my car after alternator problem

Hello everyone, I have a pontiac vibe 2005 and last week i had a problem with my alternator. My car would not start, and when my stepdad (former mechanic) checked it, he saw that the battery was full of verdigris and sulfate. We cleaned it, it still would not start. We check the alternator and saw that a small fire had started inside it (we had absolutly no notice of this, except that the car would not start), so we changed the alternator. After that my car worked for about 1 day, and now it won't start again. The alternator is brand new, i changed my starter at the begining of the year and my battery is less than 2 year old. My stepdad say that only cleaning the starter i required, but i'm afraid it won't solve the problem and i'll end up stock at work with no fonctioning car or something. Do you guys think i should just try to clean it or is it recommended to just change the starter and the battery too in case it was damaged by the faulty alternator?