The way it happened for me is that I was editing 720p 60fps video on a 720p 24fps project. I've done this on After Effects with no problem whatsoever.
I imported a folder with 24p and 60p footage to this 24p Project and as I was setting in and out points for my 60p footage the screen went black. The screen just turned off but audio was still playing. I set the in and out points by pressing the shortcuts "I" and "O." After I pressed the "O" right away the screen died. BTW I was using an iMac 21.5"...
The computer did not respond to any keystrokes or any movement of the mouse and I manually turned it off. This happened twice because I wanted to know what the problem was.
I'm guessing the problem was how I used 60p on a 24p sequence but even it that was the problem I see no reason for the screen to just die.
Anyway I would like to know anything else that you guys have in mind, in the mean time I will obviously won't edit like that again.
I'm dubious that anything you did inside of PP would actually cause your monitor to die. I'd look to a hardware or driver issue here.
I actually thought that too.
It is really weird though that as soon as I pressed O it happened and there was nothing else to do but to turn it off then on. I still also think though that it does have to do with what I was doing in PP plus the hardware that couldn't take it. This had never happened before.