When scenery is not installed for a given location, all that will be visible are airports and water. This is referred to as “water world,” and is a common problem, especially when using older installers.
To avoid water world, either install the scenery for the location in which you’re flying, or choose to fly somewhere else. To install scenery, insert the first X-Plane installation disc (the same disc used to run the simulator) and run the installer as before. Instead of installing a new copy of the program, though, when the installer window appears, press the Add or Remove Scenery button.
If scenery for the location is in fact installed, be sure that the copy of X-Plane for which it is installed is the one being used—for instance, if you have two copies of X-Plane installed (say, one running version 9.62 and one running 10.0), the two versions may have different amounts of scenery installed.