Use DDU in safe mode to clean the registry of the AMD driver, then install your desired Nvidia driver. This is a very common issue if you don't do a clean install of the GPU driver, especially when changing brands.
If that doesn't work it's probably time to do a clean install. To test if this will work simply partition your C: drive (or use a different drive or use a flash drive if you have one large enough) and do a clean install of 10 on it. Install one of the games you're having problems with. You don't need to activate 10 to do this.
Personally I'd do a clean install anyway. If you set up your files properly it can be very easy to copy/paste your data into a clean install. The Steam games folder can even be copied so you don't have to reinstall your games. When you're booted back up just install Steam, replace it's games folder with yours and have Steam verify and repair the game files (so it will launch them correctly). You can even copy/paste a game when you're doing the clean install test if you'd like.
O&O ShutUp10 is a must have tool for me (Windows10). It's standalone and doesn't run in the background. All it does is tweak the registry as you see fit or you can use their presets. Some things it does:
Prevents MS from shoving bloatware on your PC even after you've deleted it.
Prevents forced automatic updates so it doesn't change your OS at inconvenient times. You can manually update whenever you like.
Disables the telemetry data so that everything you do isn't sent to MS.
Reduces network, ram and CPU usage (quite a bit sometimes).
Windows 10 downolad (it's a toolkit for making a W10 .ISO):
Even if you have a clean copy of 10 it's best to use the latest version of the toolkit so you don't need to go through a long update process.