Where is the starter control module (unit) located ? on 2004 Volvo S40

The key will not turn, happens alot.

Asked by for the 2004 Volvo S40
If the key doesn't turn it has nothing to do with the starter.
Either the steering wheel lock is activated, and tension on the steering put pressure on the lock mechanism, in this case you need to move the steering wheel a bit while you try to turn the key. The other problem could be with the ignition lock cylinder.