Computer used to work with 16Gb of memory, now only works with 8Gb

Question

I have a rather puzzling problem, my computer used to just work for many years but now it refuses to even pass POST.

Trying to narrow down the problem, I figured out that by removing two memory modules (2 * 4Gb) it will boot flawlessly. It doesn't really matter as on which channel and which modules I do insert, they all work but only if two of them are installed at the same time.

During this investigation, I could hear continuous short beeps, sometimes, which by searching the web leads to a power supply failure. The thing is, I had a spare power supply but it yielded the same exact result so I am starting to wonder whether it could be the motherboard being the culprit.

The motherboard is a Gigabyte Z87P-D3.

Question:

Does this kind of error comes from a faulty motherboard, or is it something else?

Answer 1

"Does this kind of error comes from a faulty motherboard, or is it something else?"

Yes.

That is to say: there are many things that can cause this issue. The most likely, given the steps you have already performed, is a motherboard failure. But it could also be your CPU (the memory controller is on the CPU these days). And this kind of problem can indeed be cause by power supply and/or memory itself.

The "good" news is that the two most likely causes are the CPU and motherboard and, given that's an 4th gen Intel core CPU, you're probably going to need to replace them together and get new ram sticks to boot. It's "good" news because you won't have gamble on which one is the actual problem.