|Do you have the keyboard connected to the Purple port? If some of the keys don't work then you need to get a different keyboard.|
As mentioned above PS/2 ports are not hot swappable. Did you connect it while the computer was running?
Try shutting down for at least 20 seconds and then restart. That allows the RAM to dump.
If you have a green PS/2 port you could try using it for the keyboard. It may or may not work.
You need to be quick about tapping the required key or the computer may just skip over that option.