When the system first boots watch for a message on the screen that says PRESS F2 TO ENTER SETUP. At that point, press F2 (or whatever key it says). Let's see if the system recognizes the keyboard at that point. If it does, enter bios and look for a setting that says something along the lines of: Enable USB at boot. If you see that, enable it and reboot.
Worst case, borrow a ps2 keyboard.