CD Player works in the repair shop but not at home

My CD player had been unable to read the CDs for a long time, saying "Disc.". I had it repaired and a new laser and motor were put in. It worked perfectly at the store (where it had been tested for two days). When I got it home and connected it to my receiver, it still says "Disc." I just don't understand it. What am I doing wrong? Can the color of the RCA plugs have anything to do with it?

"Do not now seek the answers. Live the questions, resolve to be always beginning" Rilke