forced the nvidia GPU on older games, Got ERROR!

So i recently found out how to force the nvidia GPU on older games such as Half life and its mods. Well i did just that, it was playing fine until it made a freezing noise inside the game and then i got the blue screen. I did not get to read the blue screen as it had restarted before it got to the end. However, when my computer booted up again after the blue screen i tried to give it a second try at the same half life 1 game and noticed this time the GPU was not on, so i checked the nvidia settings and the half life option was locked back into the intel GPU and i was not able to choose the nvidia as i did before when i had forced it/ unlocked.

So my question is what could have possibly gone wrong to get this blue screen? the game obviously can handle the GPU. Why the crash? I'm assuming it converted back to the intel GPU because it though running the NVIDIA was bad but why? im going to try it again and see if i get this blue screen again, has anyone else encounter this problem?

Thanks!