I have a MB Pro 15'' that's almost 4 years old (=it's the previous model). I bought a Snow Leopard CD to upgrade from 10.5.8 a few days ago. I tried it on Thursday and the driver wouldn't accept it, it would try a bit to run but then it would get spitted out. I assumed it is because of the scratches the CD had. So I bought another one. And I am having the exact same problem: Although the CD is in perfect conditions, it just won't run. This time the driver tries a bit harder (I can tell by the sounds) but in the end it just won't get accepted. Any ideas about what is going wrong?