Hard crash at random times

[Mireille_Bouquet]

I tried the one monitor, setting them for same resolution and refresh, and don't get me started on GSync, monitor says it's supported, NVidia says it's supported, but it refuses to activate, even in single monitor setup.

The cable and port used on the video card and monitor can do this.
Use Display Port (not HDMI), use a very high quality DP cable (not a bundle cable provided with the card or monitor) that is rated for DP 1.4 or higher, and make sure in the event of there are multi-DP ports on the card and/or monitor(s) that you are using a port that is at minimum DP 1.4 or higher.
If the cable length is over 10 feet, make sure to go up in grade to even higher than recommended.

DP can handle the nVidia G-Sync systems (DP 1.4 and higher for anything over 120hz/FPS).
HDMI can't handle it correctly for nVidia, but does work with AMD FreeSync.