Explore the island and flip every marker switch you find to the ON (up) position.
To get clues for each Age, use the library map. Click and hold the tower icon until the beam turns red ; this rotates the physical tower behind the library to face a specific puzzle location. File: realMyst.Masterpiece.Edition.zip ...
If the game crashes, right-click the Myst.exe in your installation folder, go to Properties > Compatibility , and try setting it to Windows XP or Windows 7 . Explore the island and flip every marker switch