It all started when my wife left the lights on and the battery died. When we tried to jump start the car, it took a long time until it finally started and after a few minutes I went dead again. When the mechanic looked at the car, he realized the battery had problems, so we replaced it for a new one. Even then, the car kept refusing to start. Fuel pump is ok, there are no warning lights, we have no idea what could be the problem. Help!