as mpilchfamily says.
I was going to suggest making sure that USB legacy support is enabled in the BIOS but you will need to use a ps2 keyboard to get into the bios in the first place, so that wouldn't have been much help. :?
When you got your keyboard, did it come with a USB to ps2 converter? If you have one of these, it will save you having to get a new keyboard. Another option would be borrow a keyboard of someone who could spare it long enough for you to get set up.