New Apps no longer :S HELP!

Couple months ago, my MacBookPro started to freeze, I was getting the colorwheel for everything... to a point where i tried to start it up and it was a white screen with the apple and the loading sign. then it shut off. so i called Apple, and i restarted the whole thing, but programs like GarageBand, iPhoto, iMovie, all those cool ones were completely erased... i tried to install Snow Leopard again, but im not sure if that is what it's for.. im new to Macs and the reason why i got one was because of all those cool apps. Thanks!