OK, so, looking back over this thread...
A serial card with a PS/2 to serial adapter will not work. Those are only for PS/2 mice that can also speak RS-232, it does no actual protocol conversion, and a true PS/2 port is not an RS-232 port converted.
That PCI to USB/PS/2 card definitely won't work, as has been pointed out.
A motherboard with PS/2 on it would work.
The keyboard's clearly working on PS/2, because the adapter that the OP is using is PS/2 to USB - that is, PS/2 keyboard to USB port - and it's working AT ALL. If it didn't support PS/2, that wouldn't work. There's also not going to be a "different setting", because it's the PS/2 to USB adapter staying in boot mode that's causing this.
You need either a motherboard with PS/2 on it, or a NKRO-capable PS/2 to USB converter, such as this:
https://geekhack.org/index.php?topic=17458.0