hi mate change the glow plugs , and if its still poor there is a black box(works as a timer on how long it heats) on the passengers inner wing if that mucks up it may not start , mines went and a new one was £80 , i just got a second hand one , and keep it serviced , the 1.8td likes a good heat in the morning .
i killed mine coming up the m6 lol the keyway in the crank is crap always break , mines did on two seperate engines , in the end i throw it and stuck in a 2ltr pinto