Since it happens in YouTube and browsers try this:
Google the following: "Disable Hardware Acceleration In Chrome"
Change chrome to what you use.
I will be on my computer either browsing the web or on YouTube and all of a sudden my computer does some sort of crash. My monitor screen will be gray like it’s on still and my keyboard lights and mouse lights stay on. I have to hold the power button of my computer and restart it when this happens and then it works fine until it does this problem again. It used to make a buzzing noise from my headphones when it would do it but the past few times it hasn’t made a noise. Any idea on what could be causing it?

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