eltax cr 550?

i have the eltax cr 550 in my car, the cd player works fine, but i cannot tune the radio (its just buzzing) also i cannot get my mp3 player to work when its plugged in. I have had a friend check the wiring and he says its fine and that there may be a problem with the actual radio. as it was brought second hand i do not have the instrucion mannual for it and i cannot find it on the internet at all!
If anyone has the same radio and may know what the problem is that would be great!