Hi All I've just tried to add another 8GB to my 2008 Mac Pro system and I think it's faulty, but I just wanted to check on here before sending it back. Currently I have 10 gigs in my system in the form of 4 x 2 GB sticks and 2 x 1GB sticks that the system came with.....Leaving 2 slots free which I planned to put the 2 x 4GB sticks in that I just bought from Crucial. When I put the new memory in, the system registered 10 GB still, with the slots reading empty which I'd put the new memory in. So I took all the memory out and just put in the new stuff and the machine wouldn't boot, as well as displaying a red light inside, around where the memory trays are. Have I got bad RAM or am I missing something? What is the best configuration to slot everything? I ordered using their online helper thing (drop down menus where you select system manufacturer, model and year) and they sent me "Upgrade for an Apple Mac Pro (8-core Xeon 5400 series) 2nd Gen Early 2008 system kit of 2 CT51272AP80E.M36FH0D6" When I google the ref number associated with the RAM, it comes up with "4GB DDR2 PC2-6400 800MHz 240-Pin ECC Fully Buffered CL5 Dimm Memory Module" but when I look at my system config, the RAM there is listed as "DDR2 FB-DIMM"....Is PC2 the wrong type or doesn't that matter? Many thanks for any advice.