Ok, so I have a Mid 2009 MBP 15". I have had the standard 4gb of RAM since I first had it and was looking to upgrade. I researched online and it looks like everyone says that my MBP would support 8gb. I purchased 8gb of Corsair Vengance 204pin memory and when I installed it and went to turn on my Mac the screen stayed black and started making three beeps. It kept doing this till I had to force it to shutdown. Then after freaking out I put the old 4gb of memory back in and it boots just fine. After this I try to use one of the new 4gb chips and one of the old 2gb chips and it boots up with 6gb of RAM. I tried both of the new RAM chips on the top and bottom slot mismatched with the older memory and they work every time which means they are both in working condition. They just won't boot when they are installed at the same time. Does anyone know what may be going on? It would be VERY appreciated.