Computer not displaying video

[Theiananator]

Today, I went to watch a DVD on my computer, and I could hear the sound, but I couldn't see the video. At first I thought it might be the DVD drive, so I opened a movie that was saved on my hard drive, but alas, the same thing happened. I don't know where this came from, it was working fine yesterday. This happened once before, but I don't remember how I fixed it. Any help would be greatly appreciated.

 

[Theiananator]

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