it could be and most likely is your starter......but just to eliminate the battery try to jump it off. it could also be your ignition switch but we don't see too many of those go bad on bmw's. it honestly could be so many things but if it is your starter since this is the first time you've had this problem, if you try to start it a couple times it may start. basically in the starter you have what's called a starter solenoid, after a while the contacts that make the connection in there get burnt up and it doesn't have a good enough connection to work, sometimes you can tap the starter or try to start it like 30 times and usually you get lucky and you can drive the car to your house/shop or wherever you wanna go. if you car's a stickshift you can push it with the key to the run position and let go of the clutch in second gear and start it that way =] anyways if you need professional help message me