The simplest thing to do is to remove the cartridge and examine it. There are 3
(I think) contacts at the ends of the cartridge that mate with contacts in the
printer. Make sure they are all clean (in the cartridge and the printer), from
memory some of the ones in the printer are spring metal, make sure they are
bent out far enough to touch the cartridge contacts.
If the problem is with the door you will need to strip the printer down,
Tony
MS MVP Printing/Imaging