If you see a Reboot and Select proper Boot device. Or Insert Boot Media in Selected Boot device and press a key message on Windows 11/10, see this fix.

I'm stumped. Yesterday morning my computer was working fine. I stepped away for a few minutes, and when I came back it was on a black screen of death saying "Reboot and select proper Boot device ...

Fix PXE-E61: Media test failure, check cable, PXE-M0F: Exiting Intel PXE ROM, Exiting Intel Boot Agent errors on Windows 11/10.