My BMW 325CI will not start. The engine doesn't even turn overl

Crankshaft sensor is broken. I had exactly the same problem and after replacing that, the car now works. This sensor tells the engine when to produce the spark.

Thats not the problem. Telling the engine when to produce a spark has nothing to do with sending electricity to the starter. I have the same problem with my spare key. Lights come on, can unlock the doors, everything. But when it comes to starting the car its like you haven't even turned the key. Luckily my other key starts the car fine so my spare key is now just a backup door unlocker. There is a problem with the key and the communication between that and the cars computer that will not allow the car to start. I haven't found a solution to this even from the dealer, except buy a new key for $300 of course.

Before you do anything expensive, check your fuses. they are in the glove box.