Unable to "Duplicate" Windows 10 Screen During games.

Hi, I have GTX 1070, an Acer Predator 1440p Monitor @ 165hz, and a Samsung UA55JU6400WXXY 4K (Non- HDR) TV.

I currently have the acer plugged in via display port, and the tv plugged in via a 10 metre HDMI cord. There are no other monitors/tvs plugged in. The Acer is running in 2560 by 1440, as is the TV, although it's capable of 4k. I do not know the refresh rate of the TV, but the Acer is currently running at 165 Hz.

When i press winkey+p, I can duplicate the windows screen and whatever is on it across both screens. However, my problem is i cant get games to display on the TV and the monitor at the same time.

When I launch a game, for eg: NBA 2kXX, it will send the tv screen black, and constantly minimise the game on the pc monitor, to the taskbar. If i click on the game icon, it will try and maximise the game to full screen, before failing again and minimising it to the taskbar. I can display games fine in 1440P on either the tv or the monitor one at a time, but never simultaneously.

Does anyone know what i can do to fix this? Sometimes I wanna play games with a friend, with me at the pc desk and him at the tv on the couch. Is it due to the refresh rate in the game? ive tried turning NBA 2k14 down to 59 hz, but it didnt solve the problem.

Much Respect for anyone that knows how to fix this...

duplicate means that you need the same resolution and Hz for both of the monitors. your TV doesnt really handle 165hz so thats the problem. try running at 60Hz and you might have better results. also start with the full HD resolution to see that the cabling and stuff is working correctly.