Not sure if MSI 760GA-P43 motherboard issue or RAM issue.

Hi everyone!

Note:
from now on, I will refer to the RAM slots as
Slot_1 = A1
Slot_2 = B1
Slot_3 = A2
Slot_4 = B2

Recently I assembled a new PC for a friend of mine. The motherboard installed is a MSI 760GA-P43 with a 2x2GB DDR3 Corsair Kit @1600MHz CL8 (CMX4GX3M2A1600C8). Even if it is said in the motherboard manual to install the RAM modules into the first channel (A1 + A2) slots I ended up (subsequently to some assembling issues) installing the modules into B1 + B2. Once everything was properly assembled I installed a new Windows 8 x64 OS and everything seemed to be fine. Not much later though, my friend told me he was experiencing some random freezes (often while playing videogames such as Battlefield 3, but also while web surfing or doing random stuff). No BSODs occured, just everything froze and the very last chunk of sound started to loop. Then I tried to do a complete check-up of the whole system (both software, installing Win7 x64 and other stuff, and hardware) but I didn't find anything wrong. I also checked the RAM with MemTest obtaining three 100% PASS. So I thought that the RAMs were fine and that there could be a problem with the RAM Slots themselves. I'll refer to the first module as R1 and to the second as R2.
Here's what I got doing some tests:

Configuration 1 (initial one):
A1 -
B1 R2 (yes, R2, not a typo)
A2 -
B2 R1
Result: 4GB seen by the BIOS/OS, random freezes no BSODs. Three 100% pass with MemTest though.


Configuration 2.1:
A1 R1
B1 -
A2 -
B2 -
Result: 2GB seen by the BIOS/OS, apparently no freezes nor BSODs (no long testing in this config).

Configuration 2.2:
A1 -
B1 R1
A2 -
B2 -
Result: 2GB seen by the BIOS/OS, apparently no freezes nor BSODs (no long testing in this config).

Configuration 2.3:
A1 -
B1 -
A2 R1
B2 -
Result: 2GB seen by the BIOS/OS, apparently no freezes nor BSODs (no long testing in this config).

Configuration 2.4:
A1 -
B1 -
A2 -
B2 R1
Result: 2GB seen by the BIOS/OS, apparently no freezes nor BSODs (no long testing in this config).

Recap: Configurations from 2.1 to 2.4 are all fine.


Configuration 3.1:
A1 R2
B1 -
A2 -
B2 -
Result: The BIOS won't even make it through the POST. Black screen, no text, no beeps.

Configuration 3.2:
A1 -
B1 R2
A2 -
B2 -
Result: 2GB seen by the BIOS/OS, apparently no freezes nor BSODs (the PC is still in this config and nothing bad has happened yet).

Configuration 3.3:
A1 -
B1 -
A2 R2
B2 -
Result: The BIOS won't even make it through the POST. Black screen, no text, no beeps.

Configuration 3.4:
A1 -
B1 -
A2 -
B2 R2
Result: The BIOS won't even make it through the POST. Black screen, no text, no beeps.

Recap: R2 works only in slot B1.


Configuration 4.1:
A1 R1
B1 -
A2 R2
B2 -
Result: 2GB seen by the BIOS/OS, apparently no freezes nor BSODs. Windows says that there are 4GB but only 2GB are usable. And the task manager confirms that showing only 2GB max.

Configuration 4.2:
A1 -
B1 R1
A2 -
B2 R2
Result: 2GB seen by the BIOS/OS, apparently no freezes nor BSODs. Windows says that there are 4GB but only 2GB are usable. And the task manager confirms that showing only 2GB max. This configuration is the same as Config 1 but the RAM modules are swapped.


Configuration 5:
A1 R2
B1 -
A2 R1
B2 -
Result: The BIOS won't even make it through the POST. Black screen, no text, no beeps.

I already checked the CPU pins and there are no bent ones.
I also tried installing three DDR3 RAM modules (one by one) in Slot A1 and they all made it successfully through the POST.
(Those RAM were DDR3 Corsair Dominator @1866MHz) So I suspect it being a R2 only issue.

In conclusion: I have definitely no idea what's wrong with this PC; if it's a RAM issue with R2 or a MoBo issue. What do you think about it?
If you need any further info, please ask.

Thank you,
N00P.