Need quick help! Show tomorrow! Using video with SE--no video!

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I'm using SE version 4.3.18.  I imported an mp4 file into SE and it contains audio and video. I've set the video preferences to use a second monitor for video. In the View-Video menu I have Full Screen and Show Videos selected.  For some reason there's no video at all. And to check, I opened the original mp4 into Windows media player and it displays fine. Interestingly, when I choose "Show Audio Visualizations" the audio visual works but no video. I have everything ready for my show tomorrow and really need this to be resolved. Any help is GREATLY appreciated! Thanks!

 

Bill

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I should also add that I'm just playing the sequence right from SE, not from any show editor or anything.

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Ok, I was able to fix video. SE likes .wmv a lot more than mp4. 

New problem. I  have the desktop on my laptop set to black but SE's blank screen shows up brighter than the laptop's desktop black. Is there any way to darken SE's "black?"