Windows 10 OpenGL screen capture.

I am using C# and I am trying to make a function that will allow me to capture the game screen while I am ingame, it worked on windows XP a few years ago but since I upgraded to windows 10, all I get is black screenshots. I already searched all over the net and couldn’t find a proper solution for this. The idea is to take screenshot from counter-strike 1.6 game. Someone told me to hook the process (hl.exe) but I have no idea how to start doing this so I need a good article with an example. Thank you.