Bad Board, Bad RAM, or Something Else?

OK, So I recently upgraded my computer:
ASRock Extreme3 Gen3
Corsair XMS 1333, 16GB 4x4GB setup
Intel i7 2600 3.4GHz
Sparkle 570GTX OC
OCZ ZS 750W 80+ Bronze
Seagate 500GB 7200rpm system drive (later planning on SSD cashing with this drive)
2 Seagate 1TB 7200RPM data drives (will RAID 1 later, currently as singles)

All system temps are well within normal (assuming that the temps are reporting correctly, and I see no reason to believe that they are not). All voltages are a little high, but within what I think are acceptable limits (3.3=3.4V, 5=5.16V, 12=12.25V).

When I put the computer together it worked flawlessly for 2 weeks, and then it froze and refused to post.
1) removed GPU, still did not post
2) Reset CMOS, and watched the POST log on the mobo and it failed at 31 (Ram initialization)
3) replaced GPU, and removed 3 sticks of ram, all posted fine
4) replaced all ram, and computer worked for 15min before frezing again.
5) ran memtest86+ on each stick of RAM individually, and they all check out as fine

After trying every combination possible I have found that the system works perfectly fine so long as one specific stick of ram is removed. The stick works fine in combinations of pairs, but if there are 3 or 4 sticks of ram then this stick will not allow the system to post. The physical slots used do not make a difference.

Normally I would think without a doubt that it is simply a bad stick of RAM, except that it checks out fine when tested alone, and the motherboard has 1 minor problem of only allowing the Fan1 header to run at full speed, completely ignoring whatever setting I give it, which makes me think that there may be something wrong with the mobo.

So, what do you think? Bad RAM? Bad power regulation for the RAM on the mobo? Failing mobo? Some other idea? Thankfully the system works fine on 3 sticks of ram, but I have already run into one project that takes 12GB (just for the project, total system usage at the time was 14GB), so it would be nice to have the full 16GB back, but 12GB is more than enough for daily use.
 
Not a bad idea Oldie. I'll give that a shot when I get home this evening.
I've also contacted one of my friends who owns a PC repair store, and he is going to let me borrow a set of RAM he knows is good (4x4@1600, going to be hard to give that back lol) to make sure that it is not the Mobo. But the more I think about it, the more I am sure the RAM is at fault.
After browsing around I am finding that you have to do several runs of tests to properly test RAM. I will throw the suspicious stick in and see if memtest finds issues overnight. Thankfully the computer works fine on 3 sticks for the moment *crosses fingers*