First, simply turning on and off the printer may fix the problem. If this does not solve the problem, perform a drum reset. This may vary from printer to printer, but the basics are the same: 1.   Install the new drum. 2.   Shut the Power off and open the front cover. 3.   Press and hold the "Go" button until all the LEDs flash. For Dell Printers, press and hold the "Cancel" button.               For Okidata Printers, Press the "Menu" button three times.  4.   Turn the Power on and close the front cover. Please be aware that this will not work for every printer. To be absolutely sure how to reset the drum for your particular model, consult your service manual.