Kia sportage 2007 Won't restart after run...

I have a kia sportage 2.0 CDRI diesel. I experienced this problem a few weeks ago. After running the engine won't restart. I then usually open the oil cap cap on the engine and the cap on the transmission fluid reservoir and close them again and wait for about an hour. the engine normally restatrs after this period. I don't know if it is some heating issue or electrical issue that is causing this. It seems as if the engine compueter develops a fault and it resets after about an hour (or when the engine cools down) Please help anyone. Thanks