Laptop overheating while playing games?

I have an HP Pavilion Laptop and whenever I play games like Minecraft or TF2 it will get really hot and within 15 minutes itll overheat and shut off. Its only about a year old and I even tried plugging in a fan and pointing on my laptop but it still overheats. I put my laptop on a flat desk with nothing blocking the vents but it still does this? I leave my laptop on a lot overnight, (I torrent stuff a lot) could this be why its doing this? Or could there be dust or something in the vents blocking it?