2001 Chevy Monte Carlo No Sound, At All

Electrical problem
2001 Chevy Monte Carlo 6 cyl Front Wheel Drive 210000 miles

I had a computer replaced last year, and now I have lost my sound, ie: Stereo system as well as door chime and the control button "beeps." Once and a while for no good reason the stereo will just come on, and as suddenly as it comes on, it goes off. I suspect a wire connection somewhere, but I don't know where to look.