I have gt 840m. when I run games on Nvidia the game shows a black screen. and when I go to task manager it shows that the game doesn't respond. I switch to the integrated card and it works.
I used DDU and reinstalled the driver. tried the newest one and old versions. the issue persists.
Sounds like a laptop you're using. If you know the model it's best to use the drivers from the laptop manufacturer as those tend to use some form of switching which normal desktops don't use. Try that first to see if it helps.