I've got few high-end mechanical keyboards that comes with USB to PS/2 adapters. They were expensive and hard to find but they work flawlessly with most old motherboards connected via PS/2 port.

Recently I found this MSI small-factor computer I wanted to be my final retro PC. It's equipped with MS-6131 motherboard and to my surprise this is the only motherboard that does not support USB to PS/2 adapters. How come? I only managed to make them work for a while by connecting them at specific time during POST.

BIOS is already upgraded. Motherboard supports USB keyboards but this is not the way I wanted to use them. Is there anything I can do?