I thought my machine "died". I was at a class at the time. Turned out I had dimmed the display all the way down. Since I couldn't see the icons to press "sew" the machine wasn't going to do anything. lol! The dimmer switch (in my Janome) is right by the thread spool so I had accidentally turned it while threading the machine.
I accidentally found out what I did after unplugging and replugging the connections several times.