New components, random BSOD and reboots

I'm quite sure I have dimm slots gone bad on my motherboard.

Slots starting from near CPU are:

A1
B1
A2
B2

After running memtest for two days with both of my RAM modules, even with the old ones
it seems slots A1 and A2 are causing problems if I put a module in them.
I tried each of my two modules, even the old two modules in all four slots and everytime memtest shows up errors within a minute of the test with A1/A2 slots.
Slots B1/B2 passed 6 times with all my modules separately without errors.

Currently I have the new RAM inserted in B1/B2 and system seems stable, however the RAM isn't running dual-channel.

Yes. It worked for about a week when I first put in the new components.

Black slots are A1 and B1

Blue slots are A2 and B2

they are color coded but I only can run stable (so far) with RAM just added in B1 and B2.

I have to point out, that I also did fiddle with the bios settings to set RAM timings and voltages, even northbridge voltages manually to try and run my system stable.

After failing with those settings I just put all back to auto as they were originally.