Hi! I just bought 2 x 2Gb Ram from Crucial. http://www.crucial.com/store/partspecs.aspx?IMODULE=CT25664AC800 The problem is that my Mac doesn't start if I install them both. If I keep any of the crucial ram with the original 1Gb that came with the machine it works(and the hardware test says it is everything o.k.). I tried this setup on my MacBook too and the same result. The fan starts and the screen remains black(no biping sound). Also if I leave only one of the crucial ram the mac doesn't start. I think the problem comes from the 800Mhz of the ram module. I know they should be backwards compatible, but... you know. Should I go and switch them with 667Mhz ones? Is this really the problem or is there something I am missing? ------ Also I received a memory stick made by Adata(4Gb). On PCs the sick works fine but I cannot use it with my mac. If I want to copy something or I just keep it in the USB port, finder gives me the beach ball and says that "It was removed incorrectly". I tried to erase it or verify it with DiskUtility and the same error. Tried it on different macs - same behavior. Can I fix this? Thanks a lot!