Borrow another board to test, and test your board in another computer. If the socket is good, then motherboards are cheap. If a test board doesn't work, examine with a strong light and a magnifying glass for dirt and debris. Blow out with a couple of drops of denatured alcohol and canned air such as DustOff.
PS/2 boards seldom fail. If it is not dirt, then perhaps the cable has pulled loos from connections and is now worthless.