Recently got 4GB of RAM upgrade (not from Apple store) The RAM is DDR3 Tried to upgrade my MBP but when both chips were installed the computer wouldn't boot (made a beeping noise) tried it with one of the 2GB chips and one of the standard ones (1GB) and it booted fine. The system now says (via 'about this Mac') that it has 3GB of RAM with these mismatched chips installed and seems to work fine - so does anyone know why it won't boot with both chips? - and does this mean that it is actually only using 1GB now as it doesn't seem to like the new chips. Anyone else had a similar experience? The stickers on the new RAM read: 2GB PC3 - 10666 1333 MHZ DDR3 If that is any help. Thanks in advance for your help!