My laptop shut down several times yesterday and today for no reason I can discern. I have it on a cooling desk, so it shouldn't be overheating. It shut down again while rebooting, so I stuck it in the freezer. Which works better than throwing it out the window. When I took it out, it booted and ran startup repair, and the results were that an unspecified change to system configuration might be the problem. Uh-huh.
I've run virus scans, spyware scans, maintenance and repair, uninstalled new programs or those that have updated recently, but when I hit restart- kerblooey. I did have a microSD card in a slot for backups, and the system suddenly wouldn't let me remove it and didn't recognize that it was there. I ejected it anyway. Firefox started crashing and then wouldn't start at all, so I uninstalled that and am running Chrome just fine.
I haven't tried to reboot again to see if I still have a problem after removing the SD card, but raise your hand if you think my hard drive is just about toasted, or speak up if you have an idea I haven't tried yet.