The print cartridge contacts are dirty and the printer cannot detect a print cartridge.
Clean the contact points on the cartridges with a dry, lint-free cloth.
1. Open the top cover of the printer.
2. Remove the print cartridges.
3. Clean the copper-colored contact points on the cartridges with a dry, lint-free cloth.
NOTE: Do not wipe the nozzle end of the cartridge or touch the silver-colored nozzle plate on the bottom of the cartridge.
4. Use a dry, lint-free cloth to remove moisture from the contacts.
5. Insert the cartridges back into the printer.
6. Close the top cover.
7. Try printing again.