hey Bant !

read this whole thread......thats how i figured out it was the fuel pump relay thing that "Crossbow39" mentiones here.....like you mine cut off while driving and nothing happened when the key was turned.

Notice how when the car is cool it starts ! with no problem......its the Fuel pump relay! change that its about 220$ at the Mercedes Benz dealer.....I changed mine it took me less than five minutes and have had no problems since!! good luck!