What does it mean when the Power button light is on and one or both Printhead lights along with all other control panel lights are blinking?

This indicates a printhead issue. Ensure both printheads are properly installed, and if needed, remove the indicated printhead(s) and check that there is no plug or plastic tape on them before reinserting them securely. Also verify that you are using the correct HP printheads for your printer. (Page 2)