I think I have seen systems where, if the logon screen is left alone, it will do something on its own..but I do not remember exactly.
If you can't see anything, you might try typing in your password and hitting enter. If it sounds like it has logged in, you may still not be able to see anything, but hitting Winkey, right arrow, right arrow, u should shut it down. I get involved in things like this when I do not want to turn on my big screen in order to turn the computer off.
What type of video output do you have normally? On some occasions, HDMI outputs have been involved when a resolution changes or the type of output changes.