The computer (MacBook Pro - mid 2009) will accept only 6GB of RAM instead of 8GB.

Hi,

I have a Mid 2009 MacBook Pro that came with 4GB RAM (2 slots of 2GB each). There is room for 8GB theoretically.

I tried to upgrade my RAM with 2x4GB sticks. I know the sticks are both working and that they are the right ones for my computer.

When I use the 2 new identical 4GB sticks together, the computer beeps 3 times, pauses, and beeps 3 times again, etc., and won't turn on. They are well inserted and it has been tried many times.

When I use a combination of 1x4GB stick with one of my old 1x2GB stick, the computer turns on. But this gives me only 6GB (confirmed by the "about this mac" data).

All combinations of 1x4GB stick with 1x2GB stick (alternating slots and 4GB sticks) work, but 2x4GB doesn't. I am concluding that both slots work and could individually accept 4GB but used in combination, they don't.

Does anyone know what is going on and how I could get 8GB?

Thank you in advance for your thoughts.

natali