I believe European UGN comes with an electronic immobilizer, whereas North American counterpart without it.
Something tells me yours is the European version (not NA for sure) hence I would expect to have a coded key.
Try to start the engine with a new cut key and see what happens.
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!