if you might have spilled anything on the keyboard, your key might be dead... usually it's more than just one so check if the keys around it work. There's this cool thing that shows you if the keys are responding or not.
Go to the blue apple> System Preferences> International> Input Menu
then check on "keyboard viewier". An American Flag will show up next to the clock on the top right, go to it, then open "Show Keyboard Viewer". press keys and see if they work or not.
Also try this... Turn off your mac, then turn it back on, press and hold the mouse button (left button if you have a 2 button mouse) when you hear the mac chime and hold it. If you did it right, your CD should open up right on start-up. one the computer turns all the way on, if you press your eject key, the tray should close.