vectra starting problems

[aky5199]

Hi there i have a 1.9 cdti 120bhp vectra 57 reg it starts no problem cold if i drive a short distance and switch off and the temperature gauge hasnt moved it will turn over it wont even offer to start then i have to leave it for at least 20 mins it will start when i turn the engine over a few times can anyone tell me whats wrong please thank you r johnstone