How to re-produce the "black screen with cursor before login" issue

I came into this two days ago and it has given me a really hard time to figure out a fix.
it turned out though, the cause of my issue was probably bit different: I have two video output from the computer connect to the same monitor, one of them via a KVM. this setup had been working for a while but somehow when I rebooted my PC this time, I only get this infamous black screen death symptom, it is only after I powered off one of the monitor that I figured out that's the cause...