New 1440p Monitor Problem

Hi all,
I have just purchased a http://www.amazon.co...ailpage_o00_s00 monitor.
I Run:
i5 4670k CPU
EVGA GTX 760 GPU
Samsung 850 pro SSD.
After plugging it in and testing it with steam through CSGO and Dota ect. I booted up the Nost. Although the game would not let me play at all! as soon as I touched the mouse the frames would drop and the screen was flicking all over the place
. But when you use just the WASD there is no frame drop or anything.
With this being a 10+ year old game i thought the GPU would be fine. my question is should I send this Monitor back and go back to good old 1080p which I have been used to or get a new GPU ect?
Or is the problem due to the game settings?
What monitors are you guys rocking ? I have £300 to spend
any help would be greatly appreciated.
I have just purchased a http://www.amazon.co...ailpage_o00_s00 monitor.
I Run:
i5 4670k CPU
EVGA GTX 760 GPU
Samsung 850 pro SSD.
After plugging it in and testing it with steam through CSGO and Dota ect. I booted up the Nost. Although the game would not let me play at all! as soon as I touched the mouse the frames would drop and the screen was flicking all over the place

With this being a 10+ year old game i thought the GPU would be fine. my question is should I send this Monitor back and go back to good old 1080p which I have been used to or get a new GPU ect?
Or is the problem due to the game settings?
What monitors are you guys rocking ? I have £300 to spend
any help would be greatly appreciated.