The printhead is the part of the printer that the ink cartridges sit in. It is what sprays the ink onto the paper. I assume you must have the correct printhead, however it may be damaged or not making a good contact with the printer.
Remove the ink cartridges from your printer, then there is a grey lever that you lift up to remove the entire printhead from the computer. Clean the contacts on the printhead where it connects to the printer. Then reverse the process...put the printhead back in the printer, lower the grey lever to lock it into place and re-insert the cartridges.
New printheads can be found online, but they are expensive and with new printers running $60-100, it is sometimes a better choice to replace the printer if it will not recognize your printhead.