Radio and CD player functional, but no sound?

I am having a problem with the radio in my 2002 Lexus RX300. I had a whole new stereo system installed in it about a year ago. In the past few months, the radio and CD player would appear to be functioning, however, the sound would just go out at times. Then yesterday, I had a new battery installed and now there is no sound coming from the radio/CD player again. Is this a short, something electrical, a faulty radio, or something else? Any suggestions?