Bug/Issue Graphic issues

I'm not entirely sure if this even is a bug or my computer got a bolt loose, but I'll just explain what's going on.

Stardew Valley (no other program) tends to make my monitor go dark, then pop back up as if it just booted. This can repeat several times and also already caused a bluescreen crash. I then get a popup message telling me my g-card driver has crashed and was rebooted. Ingame rain causes weird graphic issues (black 'flakes' behaving like rain indoors), followed by already mentioned behavior.

Any idea?