Hardware trouble shooting help

I agree on all points, particularly the strange part. That is why you need to do some strange tests .

It does not make any more or less sense that every stick, tested individually, would fail at the same point because of bad RAM either.

It could be an error in the RAM controller too (And that could be voltage related). I'm not familiar with that AMD system, but I believe that the controller is on the motherboard, not in the CPU. If the PS is OK and the memory controller is throwing up errors then that could mean a bad motherboard, and, of course, we want it to be anything but that!

You know, I forgot to ask: are all of the parts in this PC 'old'? Or have you recently upgraded anything (excepting the new HDD)?

When you add RAM top a system it is important that the specs of the new and old RAM match exactly. This is particularly important when it comes to RAM voltage. Some odd things start happening when you mix-and-match RAM.

Are all 4 sticks the same spec?

Since the new sticks were installed months ago and the problem (I assume) started recently then this may not be relevant, but we see a lot of RAM errors posted here caused by mis-matched sticks, so I got to ask.