I’ve been having some trouble with my Lenovo T400 laptop recently. When under a heavy load, such as playing a game or watching a full-screen video on YouTube, the computer would spontaneously shut down without warning. I finally got fed up when it happened while playing a game, causing the saved game to become corrupted and losing several hours of progress.
I had seen these kinds of spontaneous shutdowns before on a desktop, which I eventually traced to an overheating graphics card, but had never seen this show up on a laptop before. Still, suspecting some overheating, I decided to investigate.