I've got a strange problem with a new build. I got a Antec P183 case, which got 2 case fans which can be controlled with 2 lo/mid/hi switches which are on the case already. As far as I can see, there's no 3 pin fan connector supplied on either of the fans, only 2 4-pin molex connectors.
So, only the CPU_FAN is currently connected on the mobo (no CHA_FAN or PWR_FAN connected). When I boot the system like this, CPU_LED is on, I get Q-code 19 from the mobo and it won't boot.
Now the strange thing : when I plug in a cable in the 3-pin CHA_FAN on the mobo, AND CONNECT IT TO NOTHING!, pc boots up fine... removing the cable results in the same Q-code 19 error ??
How can a cable connected to nothing make a difference ?
It sounds as though there's a self-check in place for the CHA-FAN (chassis fan) header. The only fan connection that's typically required is the CPU-FAN one. Even that self-check can be bypassed within the BIOS, though. (Or in this case, UEFI, not BIOS.)
I'd suggest connecting your open-ended cable to the CHA-FAN header then entering the UEFI and looking for options within the ASUS FAN Xpert settings to disable any possible self-check for connections to the CHA-FAN header.