MacBook wont boot after RAM change
I bought a pair of 4GB Crucial DDR3 - 1333 (PC3 10600) ram memory, I installed it but when I turn on my Mac, it doesnt start, the screen is black and emits a beep. I tried changing positions, but nothing, when I mixed one crucial and one stock ram memory, boots normally, tried with both sticks and starts normally, but Im losing 3gb of memory, what do you recommend me?
PD: Sorry for my english, Im not a native speaker.
PD2: Its a unibody MacBook White 13" mid 2010 with OS X Lion 10.7.3