let it cool down, sounds like its overheating, the funny thing with laptops is you should never use it sitting on your lap, without a tray or something, the fan cool air vents are on the bottom and out on the side, so the bottom mus always be clear, is the fan working, if so could be as i say heating up, which has a safety cut off, I have a small stand with another fan on it which plugs into a usb, keeps the laptop up and cooler,