Forum:HELP! Sims 3 Seasons emergency

Hello, I was hoping someone could help me, when I go to play the Sims 3. The Seasons expansion dominates all of expansions I already have. If I put Supernatural in the disc thing it says

Sims 3 Seasons disc must be inserted

If it helps I have a Mac, but it wasn't working so my BFF managed to get windows on there (thanks)