Mercedes Benz S430 won't start

Could be the starter solendoid. It could also be purely electrical. Have you checked the common problems for this model on RepairPal? May be helpful: http://repairpal.com/mercedes-benz-s430-2001 Otherwise, I think you'll need some good diagnostic help--especially if it's electrical.

Your key is not communicating with the car . You may need a new key.