Ok, thanks!

I still can't see how RAID settings would affect the RAM, especially since it's worked with RAM:s in all slots before, albeit 12gb. I'm not that keen on tinkering with that until I have a better understanding of what's happening, but I'm running out of ideas now.

Thanks! I was sceptical from the Crucial scan results from the start.

1.5V DDR3 is what I have - all four. These are the ones I bought:

RAM Corsair D3 1333 8GB C9 VS K2 (CMV8GX3M2A1333C9)

However, the PC won't even start past the “Acer screen” if I put just the two new ones in (which are the same make and model as the old ones that work). It's only when one of the old RAM sticks are placed in slot 0 that I can get into the BIOS and windows will start to boot (then go into the BSOD loop). I just can't make sense of this.

Yep, they're exactly the same, except for two of the digits in the part number.

So this should be the old ones (same part no.):

https://www.computersalg.se/i/617376/corsair-value-select-ddr3-modul-4-gb-dimm-240-pin-1333-mhz-pc3-10600-cl9-ej-buffrad-icke-ecc

4th letter in the part no. is “4” on the old ones, whilst the new ones have “8”. I assumed this indicates that the old ones were sold as 4gb singles whilst the new ones came as a pair (8gb).

Also, the "M1A" I reckon also indicates they're singles, and “M2A” that it's a pair.

These are my own conclusions. I could be totally wrong on these assumptions though, but it seems to make sense to me. They should be the same, and in any case they should work on their own as a pair if nothing else.

The short answer is: Yes, they're unbuffered, non-ECC and CL9.

If there's a new RAM in slot 0, I don't even get past the Acer start screen and can't get into the BIOS.

With an old RAM in slot 0 it goes into windows boot/BSOD loop - regardless of which combination and order the others are in.

So I'm not quite sure how they're actually numbered (haven't actually seen numbers on them). I read somewhere online that someone called them 0-3, so that's what I've stuck to.

Physically, there are two blue slots and two black slots, placed in the order: blue, black, blue, black. So I've assumed blue are 1 & 2, and black are 3 & 4. That would give the physical order “1-3-2-4”. It works atm with the old RAM in the blue slots, I assume this is dual channel mode.

There might be something in this though, as my RAM were placed rather strangely before all this started (and I can't remember why I placed them like that - it's been many years!) - it was Blue: 2gb - Black: 4gb - Blue: 4gb - Black: 2gb

The numbering is confusing though, and it's a bit of a guessing game. I'll see if I can snap a picture of the current setup shortly…

...and zooming in on the second picture now I actually see the numbering - it is indeed 1-3-2-4 (ie 1blue - 3black - 2blue - 4black) - with 1&2 populated.

Well, as per the mainboard markings I found yesterday after zooming in on the picture I took, blues are 1 & 2. So what they call a channel would be a combination of a blue and a black slot, if I'm not completely backwards on this…

LoL, that's the sticker on the RAM that has come off a bit - the pin's are reflecting on the surface of the RAM's sticker.

I'm pretty sure the sockets are good, since the old RAM's are working fine