1991 Chevy Camaro Computer or not?

My father gave me a 91 camaro rs that from what he believes needs a new "brain". When he bought the car it ran GREAT! But then he said it started to get warm and instead of taking it to a shop he thought he could fix the problem himself. Well fix it he did NOT!He put many hours into trying to fix it and finally gave up. So he traced all the wiring to the brain trying to find the problem when I told him to have the sensors checked. But I am a girl so what do I know right?So now it sits in my driveway with its original computer and even an alternate he had purchased at a wrecking yard or something. But the car wont run at all now. It sat for a few years which means the gas tank was probably filthy but it wants to start and backfires alot instead. And the exhaust is very strong smelling! How commen is it for the "BRAIN" to malfunction or is he just wrong all together?