It hard to tell without more information or with out being able to drive the car and experience the problem first hand. If the car drives fine in reverse but not in a forward gear the transmission may have failed. If the engine starts and maybe even idles fora little while and then stalls, the exhaust could be restricted (blocked catalytic converter), If it has no power is the Check Engine light on when the engine is running if so a scanner is needed to read codes stored in the computer of your car which will indicate where the problem is.