Release the Stop button, then press it while still holding the Power button.
If you have just refilled the ink tanks and are seeing air bubbles in the tubes, you can trigger a system-wide ink flush: canon g3400 reset
Resetting your Canon PIXMA G3400 is a common maintenance task, typically required to clear the (full ink absorber) or to restore factory settings for network troubleshooting. How to Reset the Ink Absorber (Error 5B00) Release the Stop button, then press it while