I don't think it's the PC going to sleep, he said "computer screen" so I assume it's just the monitor.
@OP It sounds like there's a software issue somewhere in your GPU for this to occur, since the moniter isn't what is bricking your PC, it's the GPU most likely. You can attempt to update your GPU drivers and it's possible it'll fix the problem, but if you're running anything recent it probably won't be addressed by the GPU driver providers.
Since it seems like you know the trigger for the issue, the obvious choice is just changing how you leave your PC. Best choice is close CoH2, but you could also manually turnoff your monitor if it has a power button and see if that changes anything. You could also try changing your monitor settings so it goes to a screensaver as opposed to fully shutting off.
Thanks bro, yeah I changed the settings. I was just wondering if anyone else was having the same issue. Cheers!