Google this and re-test with this disabled.
"How to disable Flash Hardware Acceleration?"
For the past month every time I play a Youtube video or any video full screen, red pixel boxes appear all over my screen. They continuously glitch out and then change color. Once I escape full screen the pixels disappear and my monitor is back to normal. I have a custom PC and my monitor is BenQ XL2420T and my graphics card is a GeForce GTX 680. I've gone through control panel and cleared any sketchy programs. I've gone through all the display settings and nothing is out of order. I also used a command to use the DirectX Diagnostic Tool which says that there is nothing wrong with the Graphics Card.

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