How can i fix my 1 series?

Hi Got a BMW 1 series diesel that wouldn't start. After 3 days went to the vehicle put the key in and away it started. On looking at the battery noticed one of the main leads was not pushed into the connector correct as i touched this connector the car cut out. So i then pushed the connector fully home and made sure the locking tab was locked in. Now when you get in the car the ignition comes on and the engine cranks over but will not start. Any ideas?