Computer shuts off randomly. Help!?

I've seen this a few times before.. even though your vents on the outside are clean, they are dirty on the inside around your fan.. you need a can of compressed air and spray that into the vents to remove the buildup form the inside.. it may need to be taken apart to be cleaned enoughto make it quit shutting off. But it may work. Other than that, if it doesn't work, you will have to take it in for repairs if you cant do it yourself.