As I was playing the demo, the screen would flicker every once in a while and my computer tower (Not my speakers) would beep. It was quiet, and the flicker wasn't game-halting in any way, so I thought nothing of it. After a time though, which I suspect was the time it takes for my monitor to turn itself off normally, my monitor turned off. You know, when the monitor power light goes yellow, to save energy, and you can turn it back on by moving the mouse? It did that, but neither moving the mouse nor pressing keys brought the monitor back to life. I could hear the game in the background at the time. Ctrl-Alt-Delete wouldn't work either. Nothing would bring my monitor back. It's as if Defense Grid stopped my monitor from detecting input from the computer. Very strange.