Thank you both.
I documented what Aravisian taught me as well as the permanent fix section on Swarf’s recommended site. Gonna keep the Nvidia fix suggestion as a bookmark if I need it in the future.
Removing the 750Ti did not help. But then i may have discovered why. The BIOS has a setting where if an external GPU is plugged-in, it disables the mobo integrated graphics. I disabled that to allow both GPUs to function. Then I reboot. Still on standby. On a whim, I unplugged the monitor power and replugged (the monitor also happens to be Asus). But this time I kept the monitor connected to the 750Ti instead of the mobo. Voila, it started up with full graphics. I checked for any updates and noted that Nvidia drivers are under the “other drivers” on the software updater. Then I reboot, switched off the mobo GPU again and it booted just fine.
My take - the Asus components (mobo and monitor) were being annoying. The mobo BIOS dual GPU setting (under Main->System) may have contributed but eventually this worked on the 750Ti which means the signal reception issue was a major part of the problem as Aravisian suspected. Powering the monitor off and then on again allowed it to receive signal again.
My wife is now happily on her desktop and the only machine in the house with Windows still on it is my dual boot desktop which gets powered up about once a month.
For future readers - Aravisian’s instructions in post #2 were the prerequisite to this working.