For an HP 5 that gives an Error 13 at power up (Before attempting to feed a page) check the sensor on the fuser in the back (Careful the rollers inside are hot) and the exit sensor at the top. If these are clear and working then you have to check the hard one, if you turn the printer on it's side you will see there is a slot where the paer feeds up. There is a sensor in this slot that can get a piece of paper torn off it when a paper jam is improperly cleared (Pull paper through from the inside if at all possible, avoid pulling it backwards). Usually you can clear this with a piece of cardstock to gently push the paper though from the bottom (NEVER try to push it backwards as you can break the sensor arm). I have seen cases where a label fed from the tray (Which should NEVER be done on a 4/4+/5 series) gets peeled off and stuck. In this case it is a major pain to dissassemble the printer to clear it.
Yarb