You pulled the NE lever first, then went clockwise to the last lever in the NW room? That should have removed the stone in the middle of the pentagram. If you tried that, what happened? The screen focus should pan over to the centre of the room to show the stone disappearing, IIRC.
Pulling the levers in the wrong order will cause a gargoyle to appear each time, and when all levers are pulled, the statue turns into an earth elemental rather than just being moved out of the way.
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