728i Starting problem

Hi i have a Bmw 728i se auto 1997 and it has a starting problem, the car can start first time or not start for 15 mins, the dash lights come on but starter does not make a sound. i have changed the starter and it was great for a couple of days and now the same. i have been told that there is a relay for the starter if there is where is it ?
also i have been told that it could be an inhibitor switch does this sound right, when i have had starting problems i have tried putter the car out of park and into N but still no joy.

Please help

Kind regards

paul

Does someknow if Euro/UK BMW's have the U.S. EWS 'drive away protection' system....this could be the problem. I've only thorough knowledge of U.S. spec. cars.