macbook turns off when it's hot,how's fix it?

Just days ago, when i was watching a movie with vlc, and my macbook turns off alone..!!

I feel it hot, so, just i wait some minutes and turn on again, and works..

But, again happend this, turns off, when i feel the macbook hot..

My Macbook it's mine from November 2007, and until this days, turns off alone..

I have one small app, SmcFanControl, but, i don't know what's the best profile number of rpm, to use it..

Help, please.