Nf750-g55 dimm slot 2 and 4 stoped working

ok here is the setup

amd Phenom II X4 955
2x G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666)
MSI NF750-G55
2 x evga nvidia gtx 460 se in sli
2x 60 sd Crucial in raid 0
1 tb storage drive
Rocketfish RF-900WPS - 900-Watt ATX CPU Power Supply
Windows 7 ultimate

anyway i built this pc about 2 years or less ago it was pretty much top of the line at the time. Well, a few weeks ago i decided it was time for a format re install of the os. well when it got the the copying files part and the drive spun up it just died. Well, after tearing apart and singling issues out one at a time i discovered something odd. If i took out ram from the
I I I I
No.1 No.2 No.3 No.4 No.2 and the No.3 dim slot then my computer will post in bios other wise it will not. I thought then maybe my psu was under to much of a load with light and whistles and all that going on. I bought a tester all works fine I get no -5v light but i have found on the net that newer psu don't have -5v so that is not alarm. Plus i have hooked up and 550 w i have to same results with the ram slots. So, I figured the mb gave out right? I open a new board. Then after i get the new board same thing happened with it. I have the same ram in ocz platinum so i try that ram same thing, reset bios used one vid card, used the on board vid card in my bios no matter what i do it i file all 4 dims slots it will not post. Before you even ask This board if you got look at the manual doesn't have anything called memory mapping trust me i have looked it has advance dram configuration with dram timing and cas latency and they always you to use all kinds od customized dram setting for overclocking and that type of thing witch i don't understand and have not used. I have also took the board out of the case in case a grounding issues no help there and yes the ram is good i can use the 2 and 4 slot ram in 1 and 3 slot they work fine it just the slots that are acting up and seeing how i have a new board and a old board both doing the same things. I really am at a lose the computer has had the os un installed and re install loads of times never had and problems with this before. I never post of these things because i always fix my own problems normally. But, like i said here i am with 34 gb total and only can use 8 gb total so this is getting to be a big waste PLEASE HELP!!