Error detected with the CPU fan.
Error detected with the CPU fan.
It seems you're dealing with a situation where your AIO is running at maximum fan speed continuously, causing your PC to fail to boot after shutdown. The advice from videos suggests checking the BIOS settings, but it appears your PC isn't reaching the BIOS interface and shutting down immediately after the error appears. You've already tried clearing the RTC RAM, verifying connections, and using F2 to access BIOS before power loss. Since you only reached BIOS once before it crashed again after a BIOS flash, consider trying a different approach—such as resetting the system via recovery mode or consulting advanced BIOS troubleshooting guides.
What kind of motherboard are you using? Usually it won’t power off just because the CPU fan alerts itself, unless you’ve adjusted that setting. Your AIO’s cooling unit seems to be broken, which could let the CPU get too hot and trigger a shutdown. Have you attempted to switch to a different cooler to help identify the issue?
^ This situation is handled automatically, with the shutdown feature active when no CPU fan is detected. OP shared a photo of an ASUS Sabertooth 990FX R2.0 and mentioned checking the manual online. By default, the CPU fan speed limit is set to 600 RPM; if it drops below that, a warning appears. Page 3-29. @KnowledgeByTech your image quality isn't clear—try taking another shot when you're back. I can't confirm whether the AIO pump connects to the CPU_fan header or if you own a new Corsair H100i model.
I'll refresh the photos right away once I'm back. Yep, I've been using the same AIO for several years now—it's an older model and has already been discontinued.