When you say the you have a Canon PIXMA 340, I am assuming you mean the MX340.
First, check if there is any paper, tiny bits of paper or other foreign objects jammed inside the printer (including lots of paper dust from using cheap paper). If you see nothing, turn off the printer. Unplug all cables from the unit (power, USB, etc). Wait 10 minutes. Then plug everything back in. This will of cleared the machine’s memory and done a hard reset. Turn the printer on and hopefully it works.
