You have several options.. obviously the previous posters don't know much about the sims.. anyway, here are your options..
1. Download Twallans NoCD mod- http://nraas.wikispaces.com/NoCD This will allow you to play without needing the disc
2. Do you still have the box with the code? If so register your game on origin and you will get a direct download copy of your game for FREE. Open the origin app you downloaded when you installed the game, sign in, click redeem product code, enter the code, uninstall Town Life from your computer and go back to origin, click game library, click Town Life, click download
3. Buy a more recently released Ep or Sp than Town Life your options are:
Sp's- Master Suite
Katy Perry
Diesel
70's, 80's, 90's
Eps- Pets
Showtime
Supernatural
Seasons
University Life
http://store.origin.com/store/ea/search/?keywords=the+sims+3
^Ea's official website you can buy the game and then download it to your computer
Your best option is number 2 because with 1 and 3 if you ever have to download the game again you won't be able to since you don't have the cd or the code.. Good luck