Can't launch Disk Utility upon startup
I want to initialize my mac mini to factory settings and reinstall the OS.
I found a page on the Apple support site that indicates that I need to boot the mac, and press command+r to start the Disk Utility.
What to do before you sell, give away, or trade in your Mac - Apple Support
I have only a Windows keyboard at home, so, immediately after depressing the mac mini hardware button, I press and hold the alt+r key combination.
Instead of the Disk Utility starting, the sign-in screen appears.
Mac mini, macOS High Sierra (10.13.4)