Here are the top five methods that usually work for me when working on a variety of Zebra label printers – from the GK420 and GX420 series to the bigger 110xi and M4 printers.
Step 1: power reset
Switch the printer off using the switch at the back near the power socket. Give it two seconds, then switch it back on.
Step 2: reset to factory defaults
Hold down the single round button on the front panel. The indicator light will start a flash sequence: 1, 1-2, 1-2-3, and so on. When it flashes four times, release it. This resets the printer to factory defaults. See my other post for detailed information about factory resetting.
Step 3: Label width calibration
Hold down the button until the light flashes five times, then release it. This will make the printer enter label width calibration. It will print a series of widths, getting wider each time, on a label. When the printed width matches the label width (or your preferred setting), tap the button once to lock it in.
Step 4: All other calibrations
Hold down the button until it flashes twice, then release it. This will run an automatic set of calibrations