The pilot stated his engine run-up, power application, and rotation on takeoff appeared normal until the airplane settled back onto the runway and would not respond to further pitch control inputs. He had no sensory perception of power loss, but the airplane would not fly and he lost directional control off the right side of the runway into trees. Subsequent examination of the airplane by FAA Inspectors revealed that the fuel selector valve was in the 'off' position and no fuel was in the fuel lines to the carburetor or primer.