How do you play the sims 3 late night without a disk?

Ive recently bought the sims 3 late night but i have 2 sisters who also installed it on their pc's too. Now we constantly fight about who gets to play it when and its way too expensive to buy 2 more games. I know theres a way to play it without a disk i just dont know how. Pls help! (if u give me a link for a crack pls make sure its a safe, easily downloadable one, thanx =)