Windows 10 Pro/Dell Optiplex 990
I screwed up by not leaving well enough alone.
Windows Update would not install so I tried to boot into Safe Mode with the Shift/Restart technique.
That went to a dead screen. The computer was on but the monitor screen was blank. So I restarted the computer and logged on.
Then I tried msconfig/safe boot. Big mistake.
Same thing. Computer is on but screen is blank. But since I changed the Boot in msconfig the computer is stuck booting (or better described, NOT BOOTING) in Safe Mode, ie going to a blank screen.
So now I'm stuck. I can't reboot, I can't boot to Safe Mode, and I can't get to the bios to set a boot from DVD to use the Image Repair Disc.