Diagnosis
That's the printer telling you its firmware is corrupted or failed an update. It's a software brick, not a hardware failure.
How to Fix It
You need to force a firmware reinstall. Download the latest firmware file for the LBP236dw from Canon's official support site onto a USB drive. With the printer OFF, plug the USB into the printer's port, then hold down the 'Stop' button and press the power button. Keep holding 'Stop' until you see 'Maintenance Mode' on the screen, then release. It should auto-detect the file and reflash.
If That Didn't Work
If the USB method fails or the screen stays dead, the main controller board might have a deeper fault. A full power reset is the last user step: unplug the printer from the wall for a full 30 minutes to clear any residual charge, then try the firmware process again.
Heads Up
Never interrupt a firmware update on this model. If you lose power during it, you're almost guaranteed to get this error again, and it becomes a service center fix.