Why can I not access the extra content in my Oblivion GOTY disk?

Recently I purchased the Elder Scrolls IV: Oblivion: Game of the Year Edition (Hard Copy) for the X-Box 360. I promptly installed the extra content off of the second disk and set about beating the original quest lines before moving onto the extra content. There where no issues during installation, everything went smoothly, and I was prompted to put in the first disk and play the game. Now, I have casually searched the internet trying to find what to do and so far nothing I have seen has worked for me. It just doesn't seem like the content is there though I know for a fact I installed it. Does anyone know what I need to do to resolve this? I would really like to get what I paid for here. Thank you.