Welcome to our forums, wisKeyEcHo. But you DO realize that these forums are about Macs, right? Macs don't have PS2 ports...only USB ports.
You're probably dealing with something to do with your keyboard's drivers-and since you're obviously dealing with a PC, you'd look at the Keyboard/Mouse applet in Control Panel to see what its settings are. You may also want to go into Device Manager and update or reload the keyboard driver.
Good luck with your problem!