Wife tried turning on her laptop tonight, and it's failing to boot. When she pushes the power button, it lights up like it's starting, and then immediately shuts down. Has tried this multiple times and it seems to shut off faster each time. Nothing comes on the screen in this time. It's at most 3s before it shuts off.
Probably time for the repair shop. I assume you've tried it both with external power plugged in and battery only? The fact that it shuts down so fast likely means that the processor is not even starting up which means there is no way to run a diagnostic. If there was a problem with the boot drive, that should be reported on the screen. What make/model is your laptop?