Why did my computer screen go blank and remain blank when trying to restart in normal and safe modes?

It started with kernel panic issues. Apple diagnostics reported "no issues found" but I reinstalled the OS. The problem persisted.

I took it to the Apple Store and the Logic Board was replaced. The kernel panic issues continued and I returned the computer to Apple for further tests. No hardware issues were identified.

Several KP episodes later, the screen went blank. I was able to restart it once in Safe mode and run the Apple Diagnostics program (which reported no problems).

At this point, although there is some indication something is going on, the computer will not start normally and will not start in Safe mode (the screen remains blank both times).