Dumb question, but are you plugging them in before starting the pc? Sometimes plugging into a ps/2 or unplugging one while the pc is on will cause the inputs to lock up. Without being able to go through your exact bios in person, I tried searching through screen by screen options online and couldn't find anything related to the ps/2. Unless it's something obscure like disabling usb input support or turning usb support to legacy in the bios. I've only ever had issues with activating usb peripherals in the bios to get them to recognize, not the other way around. It's not impossible, but probably unlikely that the ps/2 ports are faulty physically.