I was trying to figure out why my internal microphone wasn't working. I tried adjusting several settings, dug through the registry, searched the web for possible driver or hardware issues, updated my drivers, downgraded my drivers, and after a few days, I forgot that I'd left it outputting to my headphones in the background since it was completely silent. Mistakenly I pressed F4 and voila! It works!
#FailOfTheWeek