Why won't my Sims 3 start?

Whenever the launcher comes up and i hit the play button it keeps saying No game disc found! Please insert the Sims 3 game disc before proceeding. I've tried cleaning the disc and putting it back in many time but I can't figure out why it won't start! I have a laptop if that helps to figure out the problem. I've never had this problem before. Please help! How can I get it to work?!