I am trying to upgrade the RAM in my white macbook from 2 GB to 4GB using the RAM from a Sony VAIO laptop. If I put both 2 GB sticks from the other laptop in, my computer turns on but does not boot. The screen never turns on. If i have one of the original sticks in, and one of the new sticks in, it boots up fine and the system profiler recognizes the new RAM and says it is in working order. Why can't I boot with both sticks in? They are both DDR2 667MHz sticks and are all working.