The answer is both simple and a bit complicated at the same time.
1. You don't have drivers installed for your new GPU, this needs to happen.
2. You do NOT want to let Windows Update ever install hardware drivers. This has caused no end of misery for many users, especially for Win 10 users. IS everyone affected /... no, Are enough users affected so as to make it worth taking the effort to avoid ?... definitely yes. Win10 make it a lot worse as if you install the manufacturers drivers to correct the problem, and it works .. WU will just replace them again with the non working version. So, tiurn of the OS ability to install hardware drivers:
http://www.sevenforums.com/tutorials/82137-drivers-turn-off-automatic-driver-installation.html
http://www.tenforums.com/tutorials/15989-device-driver-automatic-installation-turn-off-windows-10-a.html
3. Follow the above steps and reboot your machine.
4. Turn off and install GFX card, connect monitor cable to your GFX card. (make sure monitor is set to correct cable type)
5. Turn on PC. Download the latest GFX card driver for your OS here:
http://www.nvidia.com/Download/index.aspx?lang=en-us
6. If you want to use nVidia's recommended game settings (recommended) and use Shadowplay, manage updates and downloads, install GeForce Experience
http://www.geforce.com/geforce-experience
7. You don't have to do anything with the OB GFX tho you could disable it in the BIOS if you choose