I had one night a few years ago where I started the night, hit play in CompuHost for the first karaoke song of the night, and the lyrics came up, but no audio. One of my definite strengths is troubleshooting, but I did everything I could think of over and over, checked and double checked, and couldn't figure it out. This went on for over an hour, and I told the bar owner that it was just going to have to be a DJ night instead of karaoke.
I kept messing with it while I played DJ sets, then at about 11:30, 2.5 hours into my show, I figured out that the volume fader in the CompuHost software was all the way down. I can't remember ever touching that, as I control practically everything with hardware and rarely mess with the audio functions of the software, but that was my issue. I think I was literally blushing with embarrassment, though everyone in the bar thought I was a genius for figuring out such a complex problem.