Does window capture not work for GAMES or for programs like google chrome? Please understand that the iGPU renders non-3D programs and if you set the GPU to use to the dGPU then try to window-grab something the iGPU is rendering, you may get problems.
And what is your laptop design? It's an HQ + 840M, so it is not a Clevo. It seems like it might be a Lenovo guessing from those specs? Either that or ASUS. I don't believe MSI makes anything satisfying your spec combination either.
Using a switchable graphics laptop means you have to choose between [monitor capture] and [window and game capture]. If you follow the instructions at
https://obsproject.com/forum/threads/laptop-black-screen-when-capturing-read-here-first.5965/ you will force OBS to run on your GeForce 840M, so window and game capture will work but monitor capture won't. You have to reverse/undo those steps so OBS runs on your integrated Intel HD4600 GPU.
The post I linked would actually cause the problem you describe, which is why I mentioned it. Do any other capture methods like window or game capture work?
I explained above, on a switchable graphics laptop you can't use all three source types. You can either use monitor capture while OBS runs on your integrated graphics hardware, or use window and game capture while OBS runs on your Nvidia graphics hardware.
It's why Optimus sucks. It's only good for battery life and introduces a ton of other issues (that most people never notice).Ah, okay. That's a shame. Thanks for the help :)