Gordon, I can't see any code that explictly places your camera in the scene. In general, it's a good idea to place everything rather than relying on defaults. That includes your camera, your matrix, all your objects.
Also, when you set SYNC ON, you must manually call SYNC or nothing is drawn to the screen. It's also a good idea to do AUTOCAM off, or else your camera gets moved to an object's location every time you create a new object.
rem Load stone floor bitmap into image
LOAD BITMAP "G.BMP",1
GET IMAGE 1,0,0,256,256
DELETE BITMAP 1
rem Activate manual syncronization and hide mouse
SYNC ON : hide mouse
AUTOCAM OFF
rem Create Matrix
MAKE MATRIX 1,1000.0,1000.0,25,25
POSITION MATRIX 1, 0,0,0
rem Texture landscape
RANDOMIZE MATRIX 1,100.0
UPDATE MATRIX 1
POSITION CAMERA 0, 10, 0
POINT CAMERA 0,0,0
rem activate and distance fogging
FOG ON
FOG COLOR rgb(256,256,256)
FOG DISTANCE 5000
rem begin loop
DO
rem control camera turrent
IF LEFTKEY()=1 THEN angle#=angle#-3.0
IF RIGHTKEY()=1 THEN angle#=angle#+3.0
rem Ensure angle stays within range
angle#=wrapvalue(angle#)
rem Update Camera angle#
YROTATE CAMERA angle#
rem Refresh Screen
SYNC
Loop
