A Mac User's Best Friend!/PLEASE READ BEFORE POSTING ANY NEW PROBLEM THREADS!!!!!!

I started playing the sims 3 on a Macbook with an internal hardrive. I lost that machine a while ago, but have since purchased a new machine, a Macbook with an SSD (External) Drive. Today, I decided to use the external DVD player to install the Sims 3 base game and Pets and Ambitions on the new machine. The DVD player installed them with no issue. However, when I try to play the game and it gets to the start new game/save game screen, it says "disc not found" although the disc is in the DVD drive, which read it good enough to install it. Any suggestions?