1. One works in the ignition
Probably dead battery. search google for bmw diamond key battery replacement.

2. one works on the door
There are 2 possible scenarios for this key.
1) previous owner dropped the key many times and transponder inside the key is damaged
2) bought the key from somewhere or used and just sync to car to lock/unlock. Since transponder in the key doesn't match EWS in the car, it won't be able to start.

Now for the brand new key you are planning to get, just go to dealer with registration and VIN. They will order new key already programmed and they will sync it. IF your EWS hasn't been changed.