First Post Here ! I have a Mac Pro 1.1 updated to 2.1 with 2 X5365 running yosemite (10.10.2) I have 4 RAM modules. It runs just fine when I have all the sticks on the first riser. If I split 2 sticks riser A two sticks riser B -> Flashing light 4 sticks riser B -> Flashing light I tried changing the sticks from one riser to the other -> same results my guess -> Bad Logic Board As there are knowledgeable people here, What should I do to either fix or confirm my problem ? Happy Xmas to all !