When you turn the car on, the servo locks up? If that's the case, it's clearly getting power. Does it move at all when you pull the throttle? What about the steering servo? It almost sounds like your failsafe kicking in, but I don't know if you're using a radio that has one or if you have an external failsafe, or none. Ghost 68 had a good idea, if your radio has failsafe built in, it's possible you accidentally reset settings.