Here's a helpful hint that will save you some time trying to figure out why your additional paper tray won't work after moving your HP printer. I recently encountered this problem after moving an HP printer to a different spot in the same office. After I plugged it back in the add on paper tray wouldn't work. Turns out, the paper tray had to have power before the printer was turned on, or the printer would not recognize it. Power applied simultaneously did not work.