I own a 2006 530i and my car won't start after pressing the start/stop button. This happened on May 4th and I had to have my car towed to the dealer. As of today, they have been unable to get the car started. They have tried the following in sequence from what they've described to me:

1) They replaced the ignition control unit which they had to have BMW Germany send them because this ignition control unit had be coded to my serial number. This didn't start the car so they put my original ignition control unit back in.
2) They then replaced what I was told is called a junction box. The Service Rep said this basically supplies power to the entire car. This didn't start the car either.
3) They then did a wire by wire / pin by pin check of the electrical system to determine if there is a short or something that is preventing the car from starting. They found nothing wrong with the electrical system through this process. At this point, they also have a BMW Factory Engineer working on my car.
4) Today, I was told they will now replace something called the megatron unit. The Service Rep stated this is a 2 piece unit which includes the control unit and the valve body. They have ordered this part and are waiting for it to arrive. However, this may or may not start the car.

So, I'm going on 2 weeks without BMW determining the actual cause of the problem. Of course, I'm quite frustrated and angry the problem hasn't been found given this is a new car and quite expensive as we all know. I figured I'd post this and see if any of you BMW owners can add any further insight. Thanks!