Before you find grandpa you need to open the last door with the glowing circles. What you need to do is align the first, the left most, inner arrow, with the outside one. Don't touch the center circle at all while doing this. Instead align the right most circle with it's outside arrow, and the center one will align itself. ALL three circles must be glowing and the door will only open if ALL the inner and outer arrows of each circle are facing each other.