Hi, my N900 was bought in the UK. The only difference is that it had faults and has now been replaced. I got it from the UK Nokia online shop. Only my replacement has got the transmitter disabled. Everything is just as described by the previous posts. I:e. just a message saying FM transmitter disabled and no options appering in media player.
I'll try run some of those things mentioned and let you know.
Could my replacement device have been meant for another country? My IMEI no begins with 3569, but my original one with the enabled transmitter did also.