don't start, battery good, it was running great, no lights on on 2003 BMW 325xi

it was running great . all of a sudden didnt start, battery is good and no dashboard lights on

2 answers
If is cranking over then have to start with basics and see what is missing when turning engine over---spark or fuel and go from there.
Take to dealer and reset the ECU it's a security thing with BMW cost bout 110.00.