The radio and CD in my S40 has stopped working

Check fuses first. Then check to see if there is power to the radio.

You need to have the system checked for a break in the MOST ring. The audio system works through fiber optic so if there is a break in the beam of light everything in the audio, navigation, satalite radio whatever it is you have will not work. Could be a faulty amp or the ICM (infotainment control module) that could be offline? You are better off taking it in to a shop that can diagnose these type of problem.