DIAGNOSIS A software glitch in the printer's firmware. It's essentially a crashed computer that needs a hard reboot.
FIX Perform a full power reset. Unplug the power cord from the back of the printer. Also, unplug the power brick from the wall outlet. Wait for 60 seconds. While unplugged, press and hold the power button on the printer for 15 seconds to drain residual power. Plug everything back in and turn the printer on.
IF THAT DIDN'T WORK The touchscreen digitizer may be faulty. As a last resort, you can try resetting the printer to factory defaults. Press and hold the 'Wireless' and 'Cancel' buttons simultaneously for 5 seconds while the printer is on. This will erase all network settings.
HEADS UP A factory reset will delete all saved Wi-Fi passwords and custom settings. You will have to set up the printer again like it's new.