To stop the radio coming on whenever you start the car you need to ensure you do the following:
1. start your car and insert your usb drive let the player start playing a track.
2. pull the usb drive out.
3. turn the radio off.
4. turn the engine off.
Next time you start the car the radio won't switch on on it's own.
To avoid it happening again, simply make certain you always remove the usb and then turn the radio off before you stop the engine.
Hope that helps.
