2003 BMW X5 hello

Electrical problem
2003 BMW X5 6 cyl Four Wheel Drive Automatic

I have a x5 3litre diesel turbo. Some times it starts some times not, but now is not starting at all, and a light stays on when I turn on the key I think the light is tracking control light, the starter works but the engine wont start if u can help me pls write me in this adress visdigitali@hotmail. Com thaks.