Myst Island -- The end. Can't open vault

Are you sure you had all of the Marker Switches turn on first?

Here is a list of the marker switches:

-on the dock, by the ship.

-by the large gears.

-by the building with the dentist chair (the planetarium).

-by the rocketship.

-by the fountain.

-by the power house.

-by the cabin.

-by the clock tower.