Not that I know such a great deal about the HP but I am beginning to think that this is not locked but actually one of the mirrors or reflectors may have a smudge or distortion or is misaligned with the scanning lens.
Things like heavy humidity may cause mould to grow on the internal surfaces.
Alternately there may be some of the light source being defused out of alignment to the lens, perhaps if yours is one that uses leds for the light source it may have blown a lamp.
If it is a neon type lamp, then I tend to think more of the mirror alignment or mirrors reflection to the receiver lens.
All of these require an internal examination and I recommend you get some one qualified to do that.
Other than that Im out of ideas. Sorry