DIAGNOSIS: Your print head is clogged, but a standard cleaning won't fix it because the clog is severe or the ink in the head has dried out.
FIX: Run a Power Cleaning cycle. On the printer's control panel, go to Setup > Maintenance > Print Head Cleaning > Deep Cleaning. This uses more ink and takes a few minutes. After it finishes, print a nozzle check pattern (also under Maintenance) to verify.
IF THAT DIDN'T WORK: The ink may have sat too long. Manually rehydrate the print head. Soak a lint-free cloth in warm distilled water, place it in the tray under the parked print head (accessed by turning off the printer and opening the front cover), and let it sit for an hour. Then run another Deep Cleaning.
HEADS UP: Repeated deep cleanings will rapidly deplete your ink cartridges. If three cycles don't work, the print head itself may need replacement—evaluate if it's cheaper to service or replace the printer.