Hello all
Updates to this puzzle:
Today I went to the school at about 2pm and the screen was with the X on it. They told me they turned it on at about 9am so it's 5 hours later. I saw it playing videos 8 hours so the screensaver theory loses ground.
I plugged in a keyboard, and when I pressed CTRL (to press CTRL-ALT-F1) the X went away and vlc resumed playing videos! The screensaver theory makes a comeback!
I checked dmesg and saw nothing unusual, no error messages (unfortunately, I didn't take a pic of the screen, will do next time).
I rebooted the machine, and less than 10 minutes later, the X screen shows up again. Screensaver theory loses ground, once again
Apparently there's no screensaver program running, but there are a few libs that might do something screensaver related.
sudo find / | grep -i screens
ps ax