Computer constantly freezes and system detects only half usable RAM

[Shaky7]

Hey all.
I recently swapped my CPU fan because the old one failed.
After that my computer started freezing under load.
Takes maybe 20 seconds in Prime95 torture test to completely freeze my computer to the point where I have to power it off manually (power button doesn't work when it freezes like that).
I found that after the fan switch Windows only used 2 out of my 4GB installed.
I thought that maybe one of my 2x2GB sticks failed so I bought new 2x4GB which I planned to buy soon anyway.
Exactly the same story after I installed new sticks, only used 4 out of 8GB and my computer still freezes under load.

What I did try:
Full reset of BIOS (took out battery)
Checked if full RAM is used in msconfig
Verify that BIOS sees both RAM's (it does)
Swapping RAM placement.
Did a 4 pass memtest from bootable USB (see pic below, no errors)





Using Windows 8.1 x64 and all the relevant specs are seen on the pictures.
Additionally I noticed that memtest also detected only 4GB of RAM even if shown that both sticks are 4GB each.
The CPU temperatures are stable even under load.

I'm thinking that the motherboard might be damaged but I want to hear opinions and tips from you guys before doing anything.

Thanks in advance.

 

[Darknecron]

What temps are you looking at with Prime95? You can use Speedfan if you need to monitor temps.

 

[Shaky7]

I assume you mean CPU. It gets to about 55 at tops under load on stock clocks.

I have made some progress but didn't solve all the problems.

With a single memory stick the computer launched and it passed 3 stages of the torture test in Prime95 so it seems to be stable that way. Tried switching the same memory to the other slot and the computer launched for few seconds and then powered off.

Seems like a bad memory slot after all.

So i have cleaned the slots and reset the BIOS once again and the good news is that now even with both sticks attached my computer doesn't seem to freeze.
No dice with 8GB RAM though it still detects only 4GB.
I've noticed that after upgrading my RAM an XMP profile option appears for them under BIOS, choosing either doesn't let me even boot and I have to reset BIOS by pulling out the battery.

This is my motherboard specs about memory
- Dual Channel DDR3 memory technology
- 2 x DDR3 DIMM slots
- Supports DDR3 2600+(OC)/2133(OC)/1866(OC)/1600/1333/1066 non-ECC, un-buffered memory
- Max. capacity of system memory: 8GB*
- Supports Intel® Extreme Memory Profile (XMP)

Additionally the sticks are 2133 by default but my computer won't boot when trying to select the correct clocks or manually enter all the RAM specs.

So no more freezes but still running on 4GB and 1333 RAM (default BIOS value).