Mobo won't post with Gskill but works in second channel

[Chalky]

Motherboard: Asus p7p55-lx
CPU: I5-760 lynnfield
Ram: SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model F3-10666CL9D-8GBXL (2x4gb)

I had built this system end of last year, no major issues however i did have to reset cmos jumper on board for it to post with the ram i had at the time which was Kingston hyperX blue 2x2gb 1333mhz (pc3-10600)

Since then I bought a dual channel kit (G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) F3-10666CL9D-8GBXL and they worked fine in the second channel (slot_b). So i wanted to swap the Gskill to slot a and remove the kingston, but the board will not post with either Gskill at all. Mem 'ok' switch on the board never seems to resolve. But, if i put the kingston back in and Gskill in slot board posts and works fine - although in Windows System it says System Ram: 12GB (6 usable).

Is this a motherboard issue do you think?

[Chalky]

Bad slot on mobo. If nothing else, at least i documented the problem for (myself).

[Tradesman]

Could try blowing out the slot with compressed air, can sometimes pick up a bit of air borne lint or hair and have it settle in a slot

[Chalky]

Thanks.

I have them both working now, go figure. The board would not post with either Gskill in channel A1. Since i'm running dual channel I want to use A1, B1. Well, I put a ram stick in B1 and it posted. Both sticks posted as singles. So then I added both sticks and it posted, but hung in windows.

From there i began to tinker with bios settings, and ended up manually setting the voltage to 1.5 manually (before that it was set to auto) and from then on it has worked perfectly. Then i applied my OC (BCLK @ 180 DRAM @1440 on stock voltages.

Since then I have set to XMP mode and am getting my best 3dmark scores, temps under load are below 50c.

I still have yet to determine what causes A1 to not post with a single stick, but will work after I post b1. I suspect a bios update should resolve this.

[Tradesman]

Glad to hear all is well, keep us posted