I just got 2 512 sticks for my mackbook and am trying to install them. I took out the two original ones and put the new ones in. I tried to turn on the computer but the LED started blinking and the computer wouldn't turn on. I opened it back up and took out one of the stick, the computer turned on normally. I opened it back up and inserted the original 256 in the empty slot and the computer wouldn't turn on. What's going on? Is the slot messed up, and if so, what should I do?