Some random thoughts:
If it prints a test page completely satisfactorily, then it seems that there's now nothing wrong with the cartridges.
Did you initiate the test print from the computer, or from the printer itself? If it was from the computer, this suggests that there's nothing wrong with the computer-printer communication, either.
Are you still getting that same error report ("cartridge missing") or does the printer just not print what you send to it?
Are you sure that the printer is set as the default?