It could have been a one time occurrence.
Another possibility is that the SD card may have been bumped so that it was no longer making proper contact. If the problem happens again, with power off, remove the SD card and then insert it again, making sure it goes straight in to its socket.
If you prefer to leave the unit powered on all the time, you might consider setting the standby brightness to a low value (or totally off) to save the display from early mortality. See the Menu page of the Brennan website where it describes the Screensaver command under the Maintenance menu.