Question HELP - Why did my computer stop posting?

Oct 23, 2020
My computer (build below) has been working normally for over two years since being first assembled. The other day when I went to turn it on, however, it wouldn't post. I have a piezo speaker hooked up and it has always beeped once. I removed the CMOS battery to clear CMOS and put back, and the computer started up successfully only once after doing so, but not immediately after. It was a few attempts to start after clearing. If relevant, the time and date displayed on my computer, when it did start that one time, was the exact time and day that I last shut down my then-working PC. So far, I have attempted to power cycle, I have replaced the CMOS battery with a fresh one, I have replaced the PSU with a new one, and I have attempted to start it under the following conditions:
  1. Take one or both RAM sticks out and/or swap them around
  2. Remove GPU and swap display to onboard HDMI port
  3. Un-seat and re-seat CPU
  4. Unplug HDD and SSD
  5. Stand the case vertically
  6. Stand the case horizontally

Some diagnostically relevant information: When I press the power button, motherboard lights come on, GPU light comes on, CPU and case fans come on and stay on, even the DVD drive is operable. It will stay in this state indefinitely - I have left it overnight like this and come back to it in the morning the same way. But the computer cannot be turned off from the power button on the case - it must be switched off at the back or unplugged. Also, I haven't had random crashes, blue screens, or any other issues with reliability until this point. Just one day, nothing.

Correct me if I'm wrong, but the no-beep/no-post would indicate that the fault is somewhere before the memory check, which would mean one of three things; PSU, mobo, or CPU. Is that right?
Seeing as I have replaced the PSU already, ensuring everything was plugged in properly, I am guessing the problem lies in the motherboard or CPU. Bad BIOS chip? Temperature probe in CPU giving faulty (too high to start) reading? Some short-circuit on the motherboard that cannot be visually identified? Bad capacitor even though all caps are flat and there is no evidence of leaking?

Any insight or further suggestions of diagnostic tests would be greatly appreciated before I throw more money at this.

Thank you,


Specs: AMD Ryzen 5 1600x
Gigabyte AB350 Gaming mobo
ASUS Strix GeForce 970
2x 8GB Corsair Vengeance DDR4 2400
Cooler Master Elite 600W PSU (new), Corsair 650W PSU (old)
Windows 10
Liquid cooled
Storage probably not relevant
Oct 23, 2020
Update: I tried to start it by jumping the PWR + and -, but with the same result. I'm not sure if this motherboard version has a backup BIOS, but I read elsewhere that you could boot into backup BIOS by holding PWR and Reset at the same time. I also tried this with the same result.