SIMS 2 PLEASE HELP!!!?

PLEASE HELP! I am trying to play the sims to bon voyage, and when i put the disk in i click on the desktop icon and hit "play". then this things pops up that says "no disk inserted. please insert the original Sims 2 Bon voyage disk"...but that disk was already in! any ideas?? is it a problem with my computer (windows) or the game?