We always have to cover "What about your files?" That is, all PC users know to backup what they can't lose but I have to always check first.

The symptom and story is typical of a banged up OS or HDD failing. It doesn't tell us which. This is why I'll get out the recovery media (which for over a decade has been our responsibility to make or obtain) then follow the maker's instruction on use. If that works you're back in business. If not you take what happens as clues to what is broken and needs replacing.