Not a good start today, I was scrolling a large document to find a peice of information to transfer to another document (another query - how-to) and my laptop shut down completely - total blackout. I managed to re-start after a few minutes, it hasn't happened before. Just looking for a comforting reasons for it acting up, hopefully we are not on our way out.
The usual cause for computer shutting down unexpectedly is overheating. (That particularly applies to laptops as they have a lot of components squeezed together into a small space, with only limited ventilation).
I recently spent quite a bit of time trying to work out why a laptop kept shutting down as I was confident that the vents weren't blocked. After wasting a few hours of my time I found that the laptop had been pushed back on a desk that had a single sheet of scrap paper on it. That piece of paper had got crumpled up behind one of the laptop's air vents, with the subsequent overheating causing the shutdowns.
Never have anything underneath a laptop which should always be placed on a hard flat surface. Using a lappy on one's lap can be fatal, as can placing the appliance on anything that is soft; such as cushions, carpets, bedclothes and tablecloths.