If you have a P/S 2 Keyboard, then the BIOS must recognize your keystrokes ...
Maybe it helps to clear your CMOS.
Well, shut down your computer, then unplug your power cable and all the other cables, now press your start button of your computer, because of residual energy.
Once you have done those steps you can open your computer's case, to gain acess to your motherboard. Remove the CR-2032 battery on the board for around 10 seconds.
Such a battery like this one:
After 10 seconds you can put your battery back in place.
Then plugin your power cable and all the other cables.
Power up your computer and try to gain acess to your BIOS with your P/S 2 keyboard (remeber that it must be plugged in, before you start your computer, well if not, it will not work).
mfg