Gear shifting problem

I have a 1999 Buick regal, 3.8 non supercharged. It stopped shifting in all gears, so I went to pull and pay bought a trans swapped it with my old one and it is still doing the same thing. So I replaced computer from pull and pay all the numbers were same I have replaced transmission with a used one, and still no shifting so I tried replacing computer and the replacement the car wont start so I don't have a proper scanner to reprogram so I need help to figure this out. I would say trans again but to get one and the exact same thing makes me think computer so that's why I replaced but I think it needs reprogramming I just need my car fixed.