Did you get the 6 quartz crystals, 3 with the compass, 3 with the camcorder?
Once you have all six, zoom into the Signal Stone and all the stones you have will be visible. If you don't have all six, search throughout the game area for the remaining crystals, then return to the Signal Stone.
Hover over parts of the stone until a hand icon is visible and you will hear a specific tone. Hover over each crystal until you hear the matching tone, left click (but don't drag) and place it at the spot on the Signal Stone that the crystal matches. Once all six are placed, you should be good to go!