Phen!ec

Since you stated that the resolution was fine using your onboard graphics I highly suggest to update your video driver (Drivers | GeForce). This should be the correct one if you use a 64 bit version of windows 10. Personally, I run WoW at 3440x1440 in fullscreen (not borderless windowed mode) and use a second display to watch twitch or browse the web. That should not be a problem either. The HDMI cable should work fine too. You used it before. Same as the HDMI input on your display.