I got a new mac pro 3.1 recently and want to upgrade hell out of it. However, to some reason, my mac pro wont start and all the memory risers on two boards keep flashing like crazy and fan got very loud. I swap around the memory all i can but it doesn't work. My mac pro 3.1 spec: 8 core 2.8ghz cpu, 20gb memory, ATI HD2600XT This is what happened exactly: 1) install Yosemite and nvidia driver 2) I found the memory can only be recognised for 16gb in Yosemite (before it's 20gb in mavericks), some memory bank has an x mark on system profile 3) I open the case install the gtx 560ti using the superdrive 4pin power, i have a 4 pin to 6 pin connector only. I also swap the memory a bit in the same time 4) it sparks and wont boot up, so i switch back to hd2600xt 5) Memory board riser start to flash crazy, no matter how i swap the memory. But it's booting up this time. So if anyone know how to fix, please let me know. Otherwise i will maybe just throw into the garbage bin. :-( Thanks a lot =============== I guess the spark may be fire the motherboard or at least the memory dimm slot both of them?