Try holding theNavigate+Loadbuttons down while turning it on... keep holding them down, as it could take quite a few seconds before the LCD saysInitializingSshould appear at the top right of the display.Press thekeys to choose theSet./Adj. Menuand press theOKkey.SERVICE MODEshould appear in the menu list and the MESSAGE LED should flash.Press the^orVkey to chooseSERVICE MODEand pressOK

Have you installed the latest firmware? Possibly there's a firmware bug that keeps it from entering Service Mode properly.You never really told us where you are, so all we can do is guess at the proper support site.Tryhttp://software.canon-europe.com/products/0010740.aspThe firmware installers there *should* find the printer on the network and install the firmware update.

According to Canon USA, the ipf650 is similar to the ipf655, ipf750 and ipf755, by the way.

You shouldn't have to enter service mode to change the printhead... however, that's what it takes to clear the error after you do change the printhead.