Windows xp desktop isnt recognizing sims 3 disc, cant install game?

Im trying to install sims 3 onto a dell windows xp desktop computer. Its not recognizing the disc, nothing happens and it doesnt appear in my computer. When I go to the cd drive in my computer and click on it it says please insert disc. But there IS a disc in. and other games work fine on it. So I cant install sims. Whats going onn?