What you need to do is that you need to open system preferences. You can do so by clicking on the icon in the dock.Then you should go to the print & fax control panel under the hardware category. Then you should select which printer do you wish to make online from the list that will appear on the left side of the screen. After that you should click on the "Open Print Queue" button. Then you should click on the "Resume Printer" button on the top of the window to change the printer from offline to online.
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