HP 1150 C Officejet

I treasure my HP 1150 C! It has served since 1995 and possibly 1000kg of paper have passed through it! Today it is starting to display “Remove and check black cartridge” and or same message with “colour”. I keep a half dozen refilled cartridges to hand and the same message comes up which ever is inserted – then all of a sudden the message is gone and all is well. Whilst in “mesage mode” it refuses to accept dox from the PC.
Any magic answers??