Try turning the key in the number 2 position to see where all the lights light up on the dash (on the bottom). If the ABS light is not lit up, then you probably just have a bad bulb. If the bulb lights up and stays on after you start the car, then you probably have a blown 10 amp fuse in the overvoltage protection relay located behind your battery behind the black plastic panel. Hope this helps.
Factory Trained Mercedes-Benz Technician