Macbook Pro Running Extremely Slow

I have a macbook pro that's only about a year and a half old. Its worked fine and suddenly yesterday day it started running so slow that I really can't use it. Every time I click on something it does the rainbow circle and takes forever to load up. I've tried cleaning it with mackeeper, restarting it. I even tried reloading snow leopard and the thing failed in the middle and said it had crashed. I really don't know what to do and I need this computer for work, please help!

Restart from your back up drive. Run the hardware test on your install DVD's. Repair the permissions. Sounds like some kind of problem with sector failure in your hard drive in critical places.