Couple hours in the game crashed, PC rebooted and suddenly the display port on my ASUS GTX 980 Strix stopped working, ruing my 2 monitor setup. I have tried installing new vBIOS, re-installing graphics drivers, but nothing worked. Been using the card for a couple of months without any previous issues. Well done Witcher....

EDIT: Not CDPR fault ofc -- just a bit annoyed that it happened after a while playing Witcher.

You're seriously blaming a game for destroying your video card? Wow.

Maybe CDPR will come out with a patch for that...

I'm guessing either you had a faulty graphics card (which happens sometimes) or the air flow of your case is crap.

Probably the just a faulty card though, I'm guessing you have warranty.

I'm sure that you have been into the nvidia geforce setup and re-enabled the 2nd monitor? If the driver was corrupted and you have replaced it then there is every chance that it has gone back to the default single monitor. Either that or it's no longer detecting that display 2 is on.
If you can't set it up in the display settings then remove both displays. use one lead from the output you think is broken and put it on one monitor. restart, if you have display then the output is working fine. Basic fault finding before you jump to conclusions.

The 2nd monitor works if I use HDMI. But the Dell I have only supports 1080p on HDMI, instead of 1440p on Display Port. I have tried to play with the settings. It even detects the monitor, just can't send any signal to it.

I have noticed that this game does drive my R9 280X (rebadged Radeon 7970), to it's maximum, so cooling is pretty important.

I however take it as a positive sign that the game engine is utilizing the GPU well; it may be that the routines aren't efficient, but at least the routines are keeping the GPU busy. As an aside, I have found Trine 2 to be the most demanding game (well GPU app) on my GPU. It is extremely stressful on the GPU system and I use it in place of OCCT, furmark or Unigine Heaven/Valley which don't seem to do as good a job at detecting instabilities and reaching a maximum temperature, where Trine 2 will.

Hmmm...

Recently my GPU would just give a black screen when switching to windows. Whatever I did, I could not get the display to appear in windows (last know good configuration, low resolution mode, etc would not work)

What I had to do, was boot into safe mode and completely remove the device driver for my display (as well as the installation files). Can you try that?

I only have a single display, so this may not help, but I would be interested to know whether these problems i've seen a couple of times on my PC are related to a failing GPU or whether there was a microsoft update that might be responsible.

Thanks for the tip, I will try it.