What are the first steps to troubleshoot error 5100 on a Canon IP2770?

Begin by turning off the printer and unplugging it from the power source. Open the printer cover and carefully check for any paper jams, loose paper scraps, or other obstructions blocking the carriage's path. Remove any visible obstacles. Also, inspect the encoder strip (a transparent plastic strip behind the carriage) for dirt or damage. Clean it gently with a dry, lint-free cloth if necessary. Plug the printer back in and turn it on to see if the error clears.