Top Row of function keys not working

Hi all, I've recently been facing this problem of having my top row of keys (ie the row containing the brightness control, volume control etc) stop working. The only 2 keys that work are the dashboard and expose keys. The rest just won't work. When this happens, i realise that i can't shut down or put my macbook pro to sleep normally as well (ie. clicking the apple logo on the menu bar and selecting the respective options). I have to then press and hold down the main power button just to switch it off... Only upon restarting can my top row keys work again.

Anyone facing this issue recently? Or any advice anyone?