Occasional Starting Problem

[chiaroscuro]

I have a 1985 300 turbo diesel. On several occasions, when I attempt to start the car, it will not start. The lights on the dash light up, including the glow plug light. When I turn the key to start, nothing happens. I only have this problem when I try to restart the car after turning it off for a short period of time, such as running into a store. It does not happen every time. Whenever I leave the car parked for a longer period of time, it fires right up. Does anyone know what might be causing this problem? Thanks for your help!!!