@plutomaniac So do you reckon the BIOS chip is faulty and needs to be replaced?

I haven't read the entire thread but the symptoms you describe @rootuser123 I've seen many times if a DIMM slot is going bad, a DIMM module is going bad, or the gold connectors need a clean. Very rarely has this issue in my experience been the cause of a faulty ROM chip and/or corrupt BIOS.

Oh ok, I will try to clean the DIMM slots with IPA.

Thanks @ket Please also go ahead and run Memtest86+ for 8-12 hours or while you sleep, that way you can further rule out faulty memory or bad memory settings.
I think either flash rom is bad or not, there is no middle ground with that. Corrupt BIOS it can't be, since you updated BIOS and have reflashed, loaded optimal, clear CMOS, loaded optimal again etc. You can try flashing older BIOS version if memory tests out OK, maybe current BIOS version has a bug?

Now the motherboard has stopped POSTing completely. I think this motherboard is a goner.

What did you do, updating anything BIOS/ME related? Go ahead and order CH341A flash programmer, when it arrives I bet we can fix this!

Nope, the board just stop POSTing completely, I think @ket is right about the memory traces between the IMC on the CPU and the DIMM slots are faulty. It has stopped POSTing completely with no display.

Sorry to hear! Get programmer before you toss it, maybe that will fix it, they're so cheap nothing to loose.

Yep does sound like a bad DIMM slot, if you can use a different kit of memory to test with that would at least rule out for certain if its the board / RAM as well as rule out simple memory compatibility problems.

Yep having issues with all known working DDR3 sticks I own.