System will only boot with one memory stick (Weird twist)

Hi everyone,

So I put a machine together for the first time a couple of weeks ago and things were running smoothly so I was a happy camper. Then, a couple of days ago I went to start up my computer and it would not POST. It would simply start up for a couple of seconds, then shut off, wait a few seconds and try all over again, and again, etc..

After troubleshooting I narrowed it down to something to do with the memory: Possibly a bad slot, maybe a bad stick, some kind of setting getting messed up in the Bios, or maybe the memory controller.

I came to this conclusion because I discovered the system will boot and run (albeit much slower) on a single stick of ram in either A2 or B2 (P8Z68-V Gen3 board), but as soon as both slots are populated, it won't POST as described above.

Here's what I've done:
-Reset all Bios settings to defaults in case a power surge thwarted my surge protector or something. I did this once with the jumper, and again by pulling the battery.

-Boot the system with either stick by itself (successful).

-Run Memtest86+ (4.2) on each stick individually. No errors. Two passes each. I've done this with each stick in slot A2 once, and B2 once.

-Plugged my two sticks into my room mate's PC and it boots up fine.

Here's the weird part: If I run memtest on either stick when they are in the A2 slot, the timings in memtest read as 9-9-9-24 which is what the RAM is advertised and listed as. If run the same test on either of them in the B2 slot, memtest shows me timings of 6-6-6-20.

In the bios, regardless of what slot either stick is in, I see 9-9-9-24.

My theory is that for some reason, the B2 slot is forcing whatever stick is in there to run at 6-6-6-20, so when I try to boot with both the A2 and B2 slot populated there is a difference in timings and it can't boot. Does this theory hold water? Or is that just a bug with memtest, displaying wrong information? If that's the case... well... I'm even more lost!

Does it sound like a bad board/memory slot? Is there a chance the memory controller (which I believe is on my CPU - i5 2500k - right?) is at fault? Any other testing suggestions?

Thanks in Advance!
-Andrew

Quick summary of the parts involved:
P8Z68-V/Gen 3
i5-2500k
Corsair Vengeance LP 1.5v DDR3

Have you checked each memory by using only 1-1 i.e. remove other 3 and try using one in each slot to test whether all the slots are working or not?

As you are having the same Mobo(as mine), I believe you already having updated BIOS.

Try A1 & B1 too. There won't be any issue on trying.

I have also checked all slot like this way. In fact I did an experiment what happens if I do so, but it creates no issue.

Thanks for the responses, guys.

I tested the A1 and B1 slots which got the same results as the A2/B2 combo. I also ran memtest a bunch more for each stick.

I switched my ram into my room mates PC and it ran fine. I switched his ram into my machine and it ran fine. The only major difference between the two sets of memory is that mine is 8gb (2x 4gb) and his is 4gb (2x 2gb).

I suspected maybe the memory controller integrated my CPU was the problem, so I tested my CPU in my room mate's machine with his and then my memory - no problems with either set. I then used his CPU in my build with first his and then my own memory and got the same results as I did with my own CPU - his memory worked, mine didn't.

From this I concluded that there has to be something wrong with the motherboard as each of my components work when used in conjunction with my room mate's motherboard.

It's strange that this issue allows me to boot the machine with 2x 2gb = 4gb but not with 2x 4gb = 8gb. Did some searching around and couldn't find any other posts stating a similar problem.

If anyone has any idea what's causing this I'd sure like to know, but regardless, it looks like I have to return the mobo and get a replacement.