So I downloaded slackware on dozens of disks.
This is no joke. When I downloaded Slackware in '95 or '96, it was over 100 3.5" floppies of 1.44 MB each. And there were still more available, those were just the ones I thought I'd need. And before you could even begin installing, each of those had to be downloaded, written and verified because floppies were not terribly reliable.
My son's Windows laptop did the same. Turns out there is a setting to make Windows truly shut down when selecting "shut down" from the menu, because normally it secretly sleeps or hibernates or something to have faster start-up times. There's also the power another device via USB option that you may have to disable in BIOS / EFI settings.