DIAGNOSIS The printer's chip on the cartridge isn't making a good connection with the contacts in the carriage, or you might have third-party cartridges that the printer is struggling to read.
FIX 1) Open the front cartridge access door. The carriage will move to the center. 2) Press down on the cartridge to release it, and take it out. 3) Look at the copper-colored contacts on the back of the cartridge and the corresponding pins inside the printer's carriage. 4) With the printer off and unplugged, use a dry cotton swab to gently wipe both sets of contacts to remove any dust or ink smudge. 5) Reinsert the cartridge, making sure you hear a firm 'click'. Close the door. The printer should cycle and recognize the cartridge.
IF THAT DIDN'T WORK If you're using third-party or remanufactured cartridges, the printer's firmware may be blocking them. Try using genuine HP 67 (black) and HP 67XL (tri-color) cartridges. If you just installed genuine HP cartridges and they're not recognized, you may have a defective cartridge—rare, but it happens.
HEADS UP Never install or remove cartridges while the printer is on and the carriage is moving. Always wait for it to park in the center and be still, or you can damage the delicate electrical contacts.