Hi!
There's one other possibility I might mention - sometimes a corrupted or failed BIOS update can cause a motherboard to be apparently dead with a halt at or during the initial POST sequence - have you tried using the m/b in an ordinary pc setup with a floppy drive and using a BIOS recovery disk? If you have and still can't get any response I'd honestly bin it or use it as an exercise in reverse-engineering and get another one the same off fleabay!!!
With the greatest of respect, I can't see why, other than a purely educational exercise, members on here attempt to try and fix pc-type motherboards as they're so plentiful and (relatively!) cheap! It's only worth doing if it's custom-made for a special piece of industrial gear and nothing else will do!
Chris Williams