Alison Lyon

I bought a 2002 LS430 from someone that had just had the transmission replaced with a used but working transmission. The problem now is that the car goes in gear but doesn't move. You can hear the motor change when you shift into reverse then again in neutral and so on but it still doesn't move. Any ideas on what the problem might be? I don't want to have to put in another transmission but if I have to I will.