How much is the radio going to cost to repair?

I suppose it is safest to check the fuses first to ensure they are OK. There is a website that has instructions on how to remove the stereo for repair http://www.carstereohelp.com/strmercedes.htm Google Mercedes factory stereo repair and your area and see if there is a repair place in your area. Call around see if there is a common problem with this radio , they will be able to give you a more accurate estimate for repair.