Hi desimaui,
Double check that you have collected all the tiles for this puzzle:
In the Right Display room with the mummy, open the drawer of the two-drawer display case to the left of the knife-case and take the white tiles.
Exit into the Centre Display room, open the cabinet here and take the black and white tiles.
Exit into the Left Display room, go along the left side of the room, open the first cabinet and take the black tiles.
That should do it.

Let us know if you still have problems.