bdcrlsn said: Have you tried using other CDs/DVDs to make sure your drive isn't going bad?
bdcrlsn said: Have you tried uninstalling and reinstalling it? If you don't want to lose your save games, copy the folder from Documents/My Games/Oblivion and you can replace it when its reinstalled.
bdcrlsn said: You shouldn't need the disk to uninstall it. You can go to the Start Menu/Control Panel/Uninstall a Program and find Oblivion on the list.