Stock stereo doesnt work anymore?

Hey I had a question about my stock stereo in my 1990 ck 1500 it use to play like radio stations and stuff but I tried putting in a cassette/ipod connector which didnt work and now it wont go back to the radio it'll just go to the cassette and make loud noises and wont stop until i turn it off I tried pressing am/fm and stuff didnt work any help?