well, it doesnt look too good im afraid..
one very simple fix might be to blow into the ps2 socket, if a wide range of keyboards work it will be a motherboard problem, but it doesnt have to be too technical to be a simple piece of dust clutterage in the socket itself.
if that fails, do you have any usb ports? (my guess is probably not seeing as its an older computer). If you dont feel like forking out money for another motherboard, i would suggest you buy a usb port card, which plugs into a spare PCI slot on your motherboard, acting as a host for usb devices. then you can buy a 15 dollar usb keyboard and plug it in, and that should work.
otherwise, ive run out of any other options you could try..