Manual or auto?
Will the key turn to the start position?
When your steering lock breaks, the wheel won't unlock. And if you've got an auto the tranny lock won't unlock either.
If you can turn the key to the start position and it unlocks the wheel & tranny (if an auto) and the battery seems to have enough power then I'd look at your ignition switch.
Really doubt you've got any problems with the cylinder or steering lock. I've had the lock break on mine. Found out that it was that after replacing the cylinder and the switch. But the only problem was the steering lock.
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build