If you bought your RAM at a place that also sells PC RAM you may have gotten mislabelled RAM. PCs can handle different RAM speeds so they’ll often label higher speed RAM as a lower speed rather than make two different speeds of RAM. But Macs are much more picky. They require a RAM stick to be exactly 1066mhz not 1333mhz. The way to tell is to put one of your old RAM sticks in and it will force the new RAM to run at the correct speed. Your MacBook requires 1066mhz RAM not 1333mhz.
These are good online stores for Mac compatible RAM
OWC http://eshop.macsales.com/shop/memory/Apple_MacBook_MacBook_Pro/Upgrade/DDR3_Whi te - They offer Mac tested RAM at very good prices.
Crucial Memory http://www.crucial.com/ - good place to buy RAM from all over the world. They also have an excellent memory selector that allows you to choose memory based on your computer's model
Data Memory Systems http://www.datamemorysystems.com/apple-memory.asp - another good, cheap place to buying RAM if you live in the U.S.
You bought the wrong speed ram, your macbook requires PC3-8500 DDR3 1066 MHz.