Such a hard/no-start condition could be that you have a glow-plug relay fuse that has broken at the molecular level [ em-brittle-ment ] and the warming up causes the fule to loose continuity over a certain range of temperature. If my guess is wrong, the only thing you are out is the ~$2.00 cost for what is a good idea anyway... a spare glow-plug relay fuse !
Mine had similar symptoms like yours and when I tested the fuse it looked OK for continuity... and then it snapped when I lightly touched it with my finger!
Let us know what you eventually find !
Sam