hmm...sounds like ghosting. Ghosting happens when you push more than one key at once and keys can sometimes stick. Look at going about buying yourself an anti-ghosting keyboard.
Im not a gamer but checked on line. Example logitech brought it up with same problem. Suggestion was check for a firmware update or keyboard manufacture update.
Just a thought.
Thanks for your input tremmor. I've tried the keyboard on other computers and it's worked perfectly fine. I'm not sure how I could find an update for a keyboard that's almost 20 yrs old. And no, I don't believe that's the reason why it's not working properly.
If its almost 20 i would trash anyway. its a cheap update.
On the otherhand it sounds like it might be a serial and not usb.
If it is a usb and works fine try a different usb port.
First, I'd try turning off "Sticky-Keys" - Either tap SHIFT 5 times rapidly, or go to your Ease of Access center and change it there. You could be inadvertently turning them on my pressing shift 5 times rapidly, in a row.
It could be a BIOS issue. My BIOS does not recognize my USB keyboard in certain menus like the menu that contains Last Known Good Configuration. I can push all the keys I want when I am in these menus and nothing happens with a USB keyboard. If I use a PS/2 keyboard everything works fine.
Check for a BIOS update. If that doesn't work try a USB keyboard on the system.