Question : Problem: Message "Print cartridge not found" HP Deskjet 820cxi

Produced a very poor colour print, leaving coloured streaks across the page as if the head was dragging, also the text was very feint with colour stains amongst the black text. If it was a dot matrix printer then some pins would be mis-firing.
After this the above "print cartridge not found" keeps re-appearing.
When you switch the printer off, the head parks on the left where I think it use  to be on the far right. When you switch it on the head ends up always in the middle with the ink light flashing. I have replaced the colour cartridge and am confident that the black is ok. You cannot print a test page, align the heads, clean the heads in fact print anything.

Answer : Problem: Message "Print cartridge not found" HP Deskjet 820cxi

Have you tried reseating the ink cartridges?
Also, the following link will help you to clean the print area
http://www.hp.com/cposupport/printers/support_doc/bpa02019.html
Random Solutions  
 
programming4us programming4us