I'm trying to upgrade my MacBook's RAM to 8GB (2x4 GB), but somehow when I install the new cards I got the 3 beeps + 5 seconds pause. The 4GB cards were already working in another early 2011 MacBook.
The point being that, if I install the memory in a mid-2009 in a 2GB+4GB configuration, the Mac runs well. I have tried to switch cards and slots and it works, too.
Does anyone know what's happening?