quick question, did you have the pc plugged into a surge protector? I truly hope that I'm wrong on this, but if you didn't and it went down during a thunderstorm, you may have some sort of damage in the pc. I would try to launch into safe mode, but no matter what you should be seeing a splash screen when you first turn on the computer, this will show up on any tv/monitor that you have the pc plugged into.
If you have an intel cpu, you could try and use the integrated graphics to see if the gpu may have had a problem.
Another thing is that windows will default to the monitor's resolution. (if you were to plug in a pc into a 480p monitor after just coming off of a 1080p monitor it will automatically switch)