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It is possible that printer lost connection with your WiFi network. You need to re-setup the printer to make it online. Download the printer software from here --> http://support-asia.canon-asia.com/contents/ASIA/EN/0100291301.html
Open/run the downloaded file and follow the instructions to setup it again.
Please let me know if that didn't work, so we can continue troubleshooting
Delete the printer from your computer. Then on your printer, go to Setup > Network and reconnect it to your wireless connection. After that, try adding it again using the printer software. Does it work now ?
On Printer, select Setup on the HOME screen. Select Wireless LAN setup. Connect it to your WiFi again. Then does your computer recognize it when you add it ?
If that didn't work, then go to Setup > LAN Settings > Reset LAN Settings. Reset it, then connect to WiFi and try to add it