Xbox 360 Unplayable disc help!?

My xbox 360 got the red ring of death, and my friend had an xbox that wouldn't read xbox 360 games, We took his apart and I put My disk tray into his xbox 360, hoping that it would work... unfortunately it didn't, when we turned it on, it said play dvd, and we had call of duty in! I put in an actual dvd, it works perfectly! I also put in a CD and it works too! Before my xbox got the red ring, My disc tray never had any problems. I am guessing it is a problem with his motherboard. I have tried about 10 new games without scratches, all the same problems. I have looked this up on youtube, I have tried about everything I could find. I am super desperate and really need some help. Thanks in advance.