When the pilot selected the landing gear down in the circuit area the gear down light failed to illuminate. He recycled the landing gear then carried out the emergency extension procedures, but without success. The aircraft was fitted with a mirror and the pilot was able to observe that although the main landing gear appeared to be down and locked, the nose landing gear had not extended. The pilot decided to divert to Gove and advised Adelaide Flight Service of his intentions. He requested that Emergency Services be made available. On arrival in the circuit area the pilot discussed the problem with company engineers, then over a period of about 30 minutes made several unsuccessful attempts to extend the nose landing gear. When the Emergency Services were in place, the pilot made an approach to runway 13. He shut down the engine on short finals, landed on the main wheels and held the nose up as long as possible. As the airspeed decreased, the nose dropped and slid along the runway, damaging the propeller and nose cowls. Subsequent investigation revealed that the nose gear doors were jamming and had trapped the nose landing gear in the up position. The aircraft had suffered a landing gear collapse during a takeoff run some months previously and had only been flown a few hours in the two months since the repair. The nose landing gear doors had been causing extension problems during that time which had not been correctly rectified.