XPS 8700, Windows 10 -- "No boot device available"

My XPS8700 (BIOS A13, Win10) is having a chronic issue of "No boot device available" upon a cold start or a reboot.

When the issue first began to surface a couple of years ago, I was able to boot successfully by going through the sequence of F2 & F10, but lately this would only works after repeated tries and seemingly like a stroke of luck.  Once booted up, the PC would run fine continuously unless/until I have to reboot for some unrelated reasons -- thus it seems like the OS disk is functioning hardware-wise.

Any pointers/suggestions would be greatly appreciated.