I had the problem with my HP Photosmart and it was a hardware fault in the scanner. It is an easy fix as it is normally in the position sensor. This is a small wheel ( looks like a strobe, but it is not) on the scan head with a light source and sensor. It can be cleaned with a soft brush or even a small strip of paper either side of the wheel. The only problem is getting to it . The screws for the scanner lid are on the underside and hard to get to. On mine the top of the printer was unscrewed (spline driver needed) and the lid lifted from the hinge. The rear screws can then be removed from the lid. Do not remove or damage the ribbon cable. With the glass removed and everything back in place the scan head can be accessed and cleaned . Test before you put it back together. If it passes the boot up self test it works.