I vote for a glow plug problem. Turn on the dome light first, and then turn the key to pre-glow. The dome light should dim. The big strip fuse at the glow plug relay can look ok and still be bad. It is a 80 amp fuse.

Don't try to spin the engine over too much until you find out what the problem is, because you can load up the engine with raw fuel which will make starting even more difficult, and create a huge mushroom cloud of smoke to impress the neighbors when it does.