My Macbook won't shutdown.

I bought my Macbook in December 2009. (MC207LL/A). Recently, it won't shut down properly if I go to the apple menu or press the power button then click shut down on the screen, it will restart the system everytime so I have to press and hold the power button to shut it down. I tried logging out and then logged in as a guest and run the disk repair but that didn't work. I also noticed if I closed the monitor down to put my mac to sleep, when I open it up, it feels quite warm below the keyboard area so I don't know if it's related to the shut down problem. I am also running a Snow Leopard / Lion partition. Booted from either partition didn't solve the shut down problem. I have to press and hold the power button everytime. Please let me know what I can do. Thank you.