Ok, so after seeing the GN video on how NOT to mount your AIO radiator, I decided to re-top mount it after buying some new 140mm high pressure fans for the front.
Admittedly, everything was running somewhat fine beforehand, but now my PC will hardly boot due to high CPU temps.
Everything is plugged in as it should be. I can feel vibration in the pump, I see lights on the pump. All that's changed is the radiator orientation.
I probably had the side mount for a couple of years before changing it today.
Any ideas?