Memory, motherboard or CPU faulty on new build ?

[acdsosys]

Only my second post, apologies if wrong section.

Recently rebuilt a Windows 8 based 'server' (backup storage facility) using a brand new AMD FX-4300, Gigabyte GA-970A-DS3P and Corsair XMS3 2x4Gb 1333Mhz.

Problem came when I tried to install Windows 8.
Unit kept freezing just after the small dots start the circle.

Tried swapping them around, tried putting them in the other 2 slots, always led to install freezing.
Then tried removing one of the sticks so I was running on a single 4Gb stick and Windows install suddenly ran with no problems.
Once Win 8 was installed and running I tried swapping the 'good' stick for the 'faulty' stick.
Not surprisingly Win 8 froze just after the dots start to circle.

At this point I was thinking "ok, dodgy stick of ram, need to send it back."

I then decided to run Memtest86 just to find out what the fault was.
Ran Memtest on the 'good' stick so i would know what to look for.
Swapped the sticks over and ran Memtest on the 'faulty' stick.
I got exactly the same 'pass' result as the 'good' stick.
I then put both sticks in again and ran Memtest a third time.
Both sticks passed all the tests ?

I will mention at this point that I tried also running my Macrium Reflect Recovery Disk which is based on WinPE 5.0 and that also froze.

I then decided to try the Corsair XMS3 2x4Gb sticks I had in another unit.
Not surprisingly, 1 stick and Windows booted but with both sticks Windows froze.
I am now thinking motherboard is also faulty!

I then tried my new sticks in the other machine and got the same result.
'good' stick Windows runs, 'faulty' stick or both sticks and Windows freezes.

Suggests faulty ram stick but if it's faulty why is Memtest86 passing it when windows can't even boot ?

I don't want to send the memory back for a replacement only to find out the motherboard is also faulty but I don't want to send both back if nothing is wrong with the motherboard.

Does anyone know of any other testing software or other things I can try which will help me narrow down what is faulty or do I just send all 3 components back on the basis all of them are faulty?