Has previously said try the glow plugs first, there should be four of them, its recomended that you change all of them at the same time, dont buy the cheap ones get a decent make, if you remove your glow plugs you can test them to see which ones work by connecting some wire to the top of the plug then earthing body of plug on battery (Warning) they get very hot, but still change all four if only one as gone as the new ones will draw more power than old ones making them less efective,or something like that...