GA-X58A-UD5 12GB Memory Problem

[snoopy]

I just built a new system with an Intel I7 950 and GA-X58A-UD5 V@ Bios version FB.  I have 12GB of Mushkin RAM, which I verified works with this board before I bought it.  The Bios sees three slots being populated, but it will NOT enable the third memory channel.  I've moved around the memory and tested dual channel -- all of which work fine.  Memtest sees the three slots being populated, too; however, it only tests 8GB.  I've loosened my CPU’s heat sink, reset the BIOS several times and tried very slow timings.  Nothing seems to help.

[Dark Mantis]

Hi and welcome to the Gigabyte UK Forum.
You say you have checked Dual Channel well if that is correct that is your problem, as you have a Triple Channel motherboard and if you have three sticks of RAM you need to be in Triple Channel Mode. It is reading only two channels rather than three hence the 8 GB rather than 12 GB.

If you have not selected this then I would think there might be a problem with the CPU socket pins. There could be some bent ones.