1997 Cadillac Catera 6 cyl Two Wheel Drive Automatic 135000 miles

i am wondering why once in a while my car radio wont play sound out the speakers, but its showing the radio is working. You can set the stations and everything and now i changed the battery yesterday morning and the radio has been working fine before that and now since its been changed it hasent had any sound come out. This is the longest its done this.. i tried to shut it off several times and press buttons but it does not help.