So, it has finally arrived. My first ever Mac. an 8 core 2.66ghz Mac Pro with 6Gig of Ram from Apple. And after years in the darkness, Boy! I am impressed. That is until I decided to get brave and install the 6x4 Gig Memory Modules I had shipped to the UK from OWC. Following all precautionary advice, I removed the Apple Ram and installed the 6 Modules in 1,2,3, & 5,6,7 just like the manual says. Put everything back together and re-booted.........Nothing! Only a flashing status light. Incidentally, no pauses between the flashes, just repeated 1 sec interval continuous blinking.........The next 5 hours I'll not bore you with, but it involved moving the memory around and trying different configurations. The most I could get recognized was 4Gig out of the 8 I had installed at that particular time. I e-mailed OWC, but am still awaiting a reply. Put the Mac Memory back in and no problem 6x1Gig instantly recognized. Today, I had another go and managed to get 16 Gig recognized at one point. I then added the other two modules (Without touching any that were already installed) and got a red LED on bay 2 & 6, which had worked ok on the previous attempt. Tried moving a few of the modules around and get the same lights lighting up. I think one module at least may be kaput, as that brings up a red LED wherever I put it. Totally frustrated by this time, I put the original 6Gig of Apple Memory in and no problems. Please, Please, Please has anyone encountered this problem before and is there a cure? Being a Newbie, is there something I should have set before upgrading to the larger RAM?...I didn't see any requirement to do this in anything I read. The modules can't all be bad, given that they have shown to be working before. What I do not understand is why a module should trigger a red LED when at the last reboot it was working ok. Any advice would be very much appreciated.