DIAGNOSIS The printer's wireless connection has dropped. Its IP address likely changed after your router was rebooted or a device conflict occurred.
FIX Re-establish the connection directly from the printer. Press and hold the Wi-Fi button until the light flashes. This puts it in connection mode. On your computer, run the Canon IJ Network Tool (installed with the drivers). It will search for and reconnect to the printer.
IF THAT DIDN'T WORK Perform a network reset on the printer. Press and hold the Wi-Fi button AND the Stop button simultaneously for 5 seconds. All lights will flash. Release. This clears all network settings. You must run the wireless setup from scratch.
HEADS UP If your router uses MAC address filtering, you must add the printer's MAC address (found on a label inside the cartridge cover) to the router's allowed list after a reset.