I had a similar problem with my PC. It has an embeedded NVIDIA GeForce 7100 / nForce 630i card. I figured there had to be a fix.
I have two video cards, so I was able to get Win10 64 bit nstalled by disabling the on-board video and using only an addon card.
Then I downloaded the NVIDIA drivers for Windows 8 64 bit. I extracted the files and shut down the computer. I reneabled the onboard video in BIOS. Windows detected it as a basic driver, but it wouldnt work. I right-clicked the setup for the Windows 8 64 bit drivers, and set compatibility mode to Windows 8. Then I installed the driver. it asked to reboot, I clicked reboot later. In Device Manager, I noticed that it showed the correct driver, but it had the yellow exclamation. I disabled it. Again click reboot later. Then enabled it. and suddenly the monitor plugged into the onboard came to life.
Good luck. I hope this works for you.