The same problem happened twice more. It seems to occur when I've pushed down the centre and right levers on the big, gray device, but not the left lever, and then try to reach the room with the large, orange electric device. It happened both when I tried to reach that room from the right and from the left. It doesn't happen when I've pushed all three levers. I'll quit playing this game for now and hope to get a solution so I can finish it later!