My HP C4280 is keeps saying that the ink cartridge is missing or is not detected even when there are both cartridges in and they are both new.

Have you removed the shipping tape from the print cartridge? It covers the print head on the cartridge to protect them so they won't leak ink.

Remove the cartridge.
Make sure that you removed a piece of clear plastic tape that covers the ink-jets. It's placed there to prevent the ink from drying-out while the cartridge has been sitting on the shelf at the computer store.
Re-insert the cartridge, and be sure that it "clicks" into place.

Uninstall the program from your computer. Plug in your printer first replace with new cartridge making sure to remover the film on the cartridge Then plug in patch cord to computer, program should reinstall if need be you may have to have your disk that comes with the printer. Hope this works, Printers are going for very cheap I would suggest buying a new one if this does not work.

You better buy a new printer.Probably you have a problem in carriage unit on your printer.

I think either the printer's scanner(or film as some call it) and/or the carriage is faulty. The signal cable that connects the carriage to the logic board could also be a suspect. Try replacing these items one after another and the culprit will be isolated. Good luck.

If these are new cartridges then you can try wiping the contacts and the pins with a dry paper towel then re install them. do not us tissue as some of them have lotion on them. If these are remanufactured cartridges return them for an exchange.

Did you run the print sample page used to align the print cartridges by scanning the test page?
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did you remove the tape from the new cartridge ?

The cartridge is not seated properly and/or the contacts are dirty. Use a cotton swab with rubbing alcohol and gently clean both the copper contacts on the cartridge and inside the cartridge socket. Allow several minutes to dry and then try again.

this link might help you
http://www.retrevo.com/s/HP-C4280-Multifunction-Printers-review-manual/id/2080dj778/t/1-2/