My first thought is a faulty ignition switch. If I understand the symptoms correctly, it sounds like the switch is providing power to the engine ignition system when in position 2, but when you put it in position 3 to start the car, the ignition switch breaks the power to the engine ignition system causing the lights to go out and failure to start. Because you only put it in position 2 to push start (and I am presuming here that is what you mean when you say jump/crash start) the car starts as normal.
If you mean it starts using jump leads, then you either have a bad connection at the battery terminals causing a high resistance or your battery is not able to provide enough power and needs replacing. If this is the case I would expect the starter motor to sound like it is struggling to turn the engine when you try to start the engine.